diff --git a/fineract-provider/src/main/java/org/apache/fineract/portfolio/loanaccount/service/reaging/LoanReAgingValidator.java b/fineract-provider/src/main/java/org/apache/fineract/portfolio/loanaccount/service/reaging/LoanReAgingValidator.java
index a3dfceb..9978514 100644
--- a/fineract-provider/src/main/java/org/apache/fineract/portfolio/loanaccount/service/reaging/LoanReAgingValidator.java
+++ b/fineract-provider/src/main/java/org/apache/fineract/portfolio/loanaccount/service/reaging/LoanReAgingValidator.java
@@ -18,18 +18,133 @@
  */
 package org.apache.fineract.portfolio.loanaccount.service.reaging;
 
+import static org.apache.fineract.infrastructure.core.service.DateUtils.getBusinessLocalDate;
+
+import java.time.LocalDate;
+import java.util.ArrayList;
+import java.util.Comparator;
+import java.util.List;
+import java.util.Optional;
 import org.apache.fineract.infrastructure.core.api.JsonCommand;
+import org.apache.fineract.infrastructure.core.data.ApiParameterError;
+import org.apache.fineract.infrastructure.core.data.DataValidatorBuilder;
+import org.apache.fineract.infrastructure.core.exception.GeneralPlatformDomainRuleException;
+import org.apache.fineract.infrastructure.core.exception.PlatformApiDataValidationException;
+import org.apache.fineract.infrastructure.core.service.DateUtils;
+import org.apache.fineract.portfolio.loanaccount.api.LoanReAgingApiConstants;
 import org.apache.fineract.portfolio.loanaccount.domain.Loan;
+import org.apache.fineract.portfolio.loanaccount.domain.LoanTransaction;
+import org.apache.fineract.portfolio.loanaccount.domain.transactionprocessor.impl.AdvancedPaymentScheduleTransactionProcessor;
+import org.apache.fineract.portfolio.loanaccount.domain.transactionprocessor.impl.ChargeOrTransaction;
+import org.apache.fineract.portfolio.loanaccount.loanschedule.domain.LoanScheduleType;
 import org.springframework.stereotype.Component;
 
 @Component
 public class LoanReAgingValidator {
 
     public void validateReAge(Loan loan, JsonCommand command) {
-        // TODO: implement
+        validateReAgeRequest(loan, command);
+        validateReAgeBusinessRules(loan);
+    }
+
+    private void validateReAgeRequest(Loan loan, JsonCommand command) {
+        List<ApiParameterError> dataValidationErrors = new ArrayList<>();
+        DataValidatorBuilder baseDataValidator = new DataValidatorBuilder(dataValidationErrors).resource("loan.reAge");
+
+        String externalId = command.stringValueOfParameterNamedAllowingNull(LoanReAgingApiConstants.externalIdParameterName);
+        baseDataValidator.reset().parameter(LoanReAgingApiConstants.externalIdParameterName).ignoreIfNull().value(externalId)
+                .notExceedingLengthOf(100);
+
+        LocalDate startDate = command.localDateValueOfParameterNamed(LoanReAgingApiConstants.startDate);
+        baseDataValidator.reset().parameter(LoanReAgingApiConstants.startDate).value(startDate).notNull()
+                .validateDateAfter(loan.getMaturityDate());
+
+        String frequencyType = command.stringValueOfParameterNamedAllowingNull(LoanReAgingApiConstants.frequencyType);
+        baseDataValidator.reset().parameter(LoanReAgingApiConstants.frequencyType).value(frequencyType).notNull();
+
+        Integer frequencyNumber = command.integerValueOfParameterNamed(LoanReAgingApiConstants.frequencyNumber);
+        baseDataValidator.reset().parameter(LoanReAgingApiConstants.frequencyNumber).value(frequencyNumber).notNull()
+                .integerGreaterThanZero();
+
+        Integer numberOfInstallments = command.integerValueOfParameterNamed(LoanReAgingApiConstants.numberOfInstallments);
+        baseDataValidator.reset().parameter(LoanReAgingApiConstants.numberOfInstallments).value(numberOfInstallments).notNull()
+                .integerGreaterThanZero();
+
+        throwExceptionIfValidationErrorsExist(dataValidationErrors);
+    }
+
+    private void validateReAgeBusinessRules(Loan loan) {
+        // validate reaging shouldn't happen before maturity
+        if (DateUtils.isBefore(getBusinessLocalDate(), loan.getMaturityDate())) {
+            throw new GeneralPlatformDomainRuleException("error.msg.loan.reage.cannot.be.submitted.before.maturity",
+                    "Loan cannot be re-aged before maturity", loan.getId());
+        }
+
+        // validate reaging is only available for progressive schedule & advanced payment allocation
+        LoanScheduleType loanScheduleType = LoanScheduleType.valueOf(loan.getLoanProductRelatedDetail().getLoanScheduleType().name());
+        boolean isProgressiveSchedule = LoanScheduleType.PROGRESSIVE.equals(loanScheduleType);
+
+        String transactionProcessingStrategyCode = loan.getTransactionProcessingStrategyCode();
+        boolean isAdvancedPaymentSchedule = AdvancedPaymentScheduleTransactionProcessor.ADVANCED_PAYMENT_ALLOCATION_STRATEGY
+                .equals(transactionProcessingStrategyCode);
+
+        if (!(isProgressiveSchedule && isAdvancedPaymentSchedule)) {
+            throw new GeneralPlatformDomainRuleException("error.msg.loan.reage.supported.only.for.progressive.loan.schedule.type",
+                    "Loan reaging is only available for progressive repayment schedule and Advanced payment allocation strategy",
+                    loan.getId());
+        }
+
+        // validate reaging is only available for non-interest bearing loans
+        if (loan.isInterestBearing()) {
+            throw new GeneralPlatformDomainRuleException("error.msg.loan.reage.supported.only.for.non.interest.loans",
+                    "Loan reaging is only available for non-interest bearing loans", loan.getId());
+        }
+
+        // validate reaging is only done on an active loan
+        if (!loan.getStatus().isActive()) {
+            throw new GeneralPlatformDomainRuleException("error.msg.loan.reage.supported.only.for.active.loans",
+                    "Loan reaging can only be done on active loans", loan.getId());
+        }
+
+        // validate if there's already a re-aging transaction for today
+        boolean isReAgingTransactionForTodayPresent = loan.getLoanTransactions().stream()
+                .anyMatch(tx -> tx.getTypeOf().isReAge() && tx.getTransactionDate().equals(getBusinessLocalDate()));
+        if (isReAgingTransactionForTodayPresent) {
+            throw new GeneralPlatformDomainRuleException("error.msg.loan.reage.reage.transaction.already.present.for.today",
+                    "Loan reaging can only be done once a day. There has already been a reaging done for today", loan.getId());
+        }
     }
 
     public void validateUndoReAge(Loan loan, JsonCommand command) {
-        // TODO: implement
+        validateUndoReAgeBusinessRules(loan);
+    }
+
+    private void validateUndoReAgeBusinessRules(Loan loan) {
+        // validate if there's a reaging transaction already
+        Optional<LoanTransaction> optionalReAgingTx = loan.getLoanTransactions().stream().filter(tx -> tx.getTypeOf().isReAge())
+                .min(Comparator.comparing(LoanTransaction::getTransactionDate));
+        if (optionalReAgingTx.isEmpty()) {
+            throw new GeneralPlatformDomainRuleException("error.msg.loan.reage.reaging.transaction.missing",
+                    "Undoing a reaging can only be done if there was a reaging already", loan.getId());
+        }
+
+        // validate if there's no payment between the reaging and today
+        boolean repaymentExistsAfterReAging = loan.getLoanTransactions().stream()
+                .anyMatch(tx -> tx.getTypeOf().isRepaymentType() && transactionHappenedAfterOther(tx, optionalReAgingTx.get()));
+        if (repaymentExistsAfterReAging) {
+            throw new GeneralPlatformDomainRuleException("error.msg.loan.reage.repayment.exists.after.reaging",
+                    "Undoing a reaging can only be done if there hasn't been any repayment afterwards", loan.getId());
+        }
+    }
+
+    private void throwExceptionIfValidationErrorsExist(List<ApiParameterError> dataValidationErrors) {
+        if (!dataValidationErrors.isEmpty()) {
+            throw new PlatformApiDataValidationException("validation.msg.validation.errors.exist", "Validation errors exist.",
+                    dataValidationErrors);
+        }
+    }
+
+    private boolean transactionHappenedAfterOther(LoanTransaction transaction, LoanTransaction otherTransaction) {
+        return new ChargeOrTransaction(transaction).compareTo(new ChargeOrTransaction(otherTransaction)) > 0;
     }
 }
diff --git a/fineract-provider/src/test/java/org/apache/fineract/portfolio/loanaccount/service/reaging/LoanReAgingValidatorTest.java b/fineract-provider/src/test/java/org/apache/fineract/portfolio/loanaccount/service/reaging/LoanReAgingValidatorTest.java
new file mode 100644
index 0000000..950c7e8
--- /dev/null
+++ b/fineract-provider/src/test/java/org/apache/fineract/portfolio/loanaccount/service/reaging/LoanReAgingValidatorTest.java
@@ -0,0 +1,507 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements. See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership. The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied. See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+package org.apache.fineract.portfolio.loanaccount.service.reaging;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+import static org.mockito.BDDMockito.given;
+import static org.mockito.Mockito.mock;
+
+import java.time.Clock;
+import java.time.LocalDate;
+import java.time.LocalTime;
+import java.time.OffsetDateTime;
+import java.time.ZoneOffset;
+import java.time.format.DateTimeFormatter;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+import org.apache.commons.lang3.RandomStringUtils;
+import org.apache.fineract.infrastructure.businessdate.domain.BusinessDateType;
+import org.apache.fineract.infrastructure.core.api.JsonCommand;
+import org.apache.fineract.infrastructure.core.domain.ActionContext;
+import org.apache.fineract.infrastructure.core.domain.FineractPlatformTenant;
+import org.apache.fineract.infrastructure.core.exception.GeneralPlatformDomainRuleException;
+import org.apache.fineract.infrastructure.core.exception.PlatformApiDataValidationException;
+import org.apache.fineract.infrastructure.core.serialization.FromJsonHelper;
+import org.apache.fineract.infrastructure.core.service.ThreadLocalContextUtil;
+import org.apache.fineract.portfolio.loanaccount.domain.Loan;
+import org.apache.fineract.portfolio.loanaccount.domain.LoanStatus;
+import org.apache.fineract.portfolio.loanaccount.domain.LoanTransaction;
+import org.apache.fineract.portfolio.loanaccount.domain.LoanTransactionType;
+import org.apache.fineract.portfolio.loanaccount.domain.transactionprocessor.impl.AdvancedPaymentScheduleTransactionProcessor;
+import org.apache.fineract.portfolio.loanaccount.domain.transactionprocessor.impl.DuePenFeeIntPriInAdvancePriPenFeeIntLoanRepaymentScheduleTransactionProcessor;
+import org.apache.fineract.portfolio.loanaccount.loanschedule.domain.LoanScheduleType;
+import org.apache.fineract.portfolio.loanproduct.domain.LoanProductRelatedDetail;
+import org.junit.jupiter.api.AfterEach;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+class LoanReAgingValidatorTest {
+
+    public static final String DATE_FORMAT = "dd MMMM yyyy";
+    private final LocalDate actualDate = LocalDate.now(Clock.systemUTC());
+    private final LocalDate maturityDate = actualDate.plusDays(30);
+    private final LocalDate businessDate = maturityDate.plusDays(1);
+    private final LocalDate afterMaturity = maturityDate.plusDays(7);
+
+    private LoanReAgingValidator underTest = new LoanReAgingValidator();
+
+    @BeforeEach
+    public void setUp() {
+        ThreadLocalContextUtil.setTenant(new FineractPlatformTenant(1L, "default", "Default", "Asia/Kolkata", null));
+        ThreadLocalContextUtil.setActionContext(ActionContext.DEFAULT);
+        ThreadLocalContextUtil.setBusinessDates(new HashMap<>(Map.of(BusinessDateType.BUSINESS_DATE, businessDate)));
+    }
+
+    @AfterEach
+    public void tearDown() {
+        ThreadLocalContextUtil.reset();
+    }
+
+    @Test
+    public void testValidateReAge_ShouldNotThrowException() {
+        // given
+        Loan loan = loan();
+        JsonCommand command = jsonCommand();
+        // when
+        underTest.validateReAge(loan, command);
+        // then no exception thrown
+    }
+
+    @Test
+    public void testValidateReAge_ShouldThrowException_WhenExternalIdIsLongerThan100() {
+        // given
+        Loan loan = loan();
+        JsonCommand command = jsonCommand(RandomStringUtils.randomAlphabetic(120));
+        // when
+        PlatformApiDataValidationException result = assertThrows(PlatformApiDataValidationException.class,
+                () -> underTest.validateReAge(loan, command));
+        // then
+        assertThat(result).isNotNull();
+        assertThat(result.getGlobalisationMessageCode()).isEqualTo("validation.msg.validation.errors.exist");
+        assertThat(result.getErrors().get(0).getUserMessageGlobalisationCode())
+                .isEqualTo("validation.msg.loan.reAge.externalId.exceeds.max.length");
+    }
+
+    @Test
+    public void testValidateReAge_ShouldThrowException_WhenStartDateIsMissing() {
+        // given
+        Loan loan = loan();
+        JsonCommand command = makeJsonCommand("""
+                {
+                    "externalId": "12345",
+                    "dateFormat": "%s",
+                    "locale": "en",
+                    "frequencyType": "MONTHS",
+                    "frequencyNumber": 1,
+                    "numberOfInstallments": 1
+                }
+                """.formatted(DATE_FORMAT));
+        // when
+        PlatformApiDataValidationException result = assertThrows(PlatformApiDataValidationException.class,
+                () -> underTest.validateReAge(loan, command));
+        // then
+        assertThat(result).isNotNull();
+        assertThat(result.getGlobalisationMessageCode()).isEqualTo("validation.msg.validation.errors.exist");
+        assertThat(result.getErrors().get(0).getUserMessageGlobalisationCode())
+                .isEqualTo("validation.msg.loan.reAge.startDate.cannot.be.blank");
+    }
+
+    @Test
+    public void testValidateReAge_ShouldThrowException_WhenFrequencyTypeIsMissing() {
+        // given
+        Loan loan = loan();
+        JsonCommand command = makeJsonCommand("""
+                {
+                    "externalId": "12345",
+                    "dateFormat": "%s",
+                    "locale": "en",
+                    "startDate": "%s",
+                    "frequencyNumber": 1,
+                    "numberOfInstallments": 1
+                }
+                """.formatted(DATE_FORMAT, formatDate(afterMaturity)));
+        // when
+        PlatformApiDataValidationException result = assertThrows(PlatformApiDataValidationException.class,
+                () -> underTest.validateReAge(loan, command));
+        // then
+        assertThat(result).isNotNull();
+        assertThat(result.getGlobalisationMessageCode()).isEqualTo("validation.msg.validation.errors.exist");
+        assertThat(result.getErrors().get(0).getUserMessageGlobalisationCode())
+                .isEqualTo("validation.msg.loan.reAge.frequencyType.cannot.be.blank");
+    }
+
+    @Test
+    public void testValidateReAge_ShouldThrowException_WhenFrequencyNumberIsMissing() {
+        // given
+        Loan loan = loan();
+        JsonCommand command = makeJsonCommand("""
+                {
+                    "externalId": "12345",
+                    "dateFormat": "%s",
+                    "locale": "en",
+                    "startDate": "%s",
+                    "frequencyType": "MONTHS",
+                    "numberOfInstallments": 1
+                }
+                """.formatted(DATE_FORMAT, formatDate(afterMaturity)));
+        // when
+        PlatformApiDataValidationException result = assertThrows(PlatformApiDataValidationException.class,
+                () -> underTest.validateReAge(loan, command));
+        // then
+        assertThat(result).isNotNull();
+        assertThat(result.getGlobalisationMessageCode()).isEqualTo("validation.msg.validation.errors.exist");
+        assertThat(result.getErrors().get(0).getUserMessageGlobalisationCode())
+                .isEqualTo("validation.msg.loan.reAge.frequencyNumber.cannot.be.blank");
+    }
+
+    @Test
+    public void testValidateReAge_ShouldThrowException_WhenFrequencyNumberIsZero() {
+        // given
+        Loan loan = loan();
+        JsonCommand command = makeJsonCommand("""
+                {
+                    "externalId": "12345",
+                    "dateFormat": "%s",
+                    "locale": "en",
+                    "startDate": "%s",
+                    "frequencyType": "MONTHS",
+                    "frequencyNumber": 0,
+                    "numberOfInstallments": 1
+                }
+                """.formatted(DATE_FORMAT, formatDate(afterMaturity)));
+        // when
+        PlatformApiDataValidationException result = assertThrows(PlatformApiDataValidationException.class,
+                () -> underTest.validateReAge(loan, command));
+        // then
+        assertThat(result).isNotNull();
+        assertThat(result.getGlobalisationMessageCode()).isEqualTo("validation.msg.validation.errors.exist");
+        assertThat(result.getErrors().get(0).getUserMessageGlobalisationCode())
+                .isEqualTo("validation.msg.loan.reAge.frequencyNumber.not.greater.than.zero");
+    }
+
+    @Test
+    public void testValidateReAge_ShouldThrowException_WhenNumberOfInstallmentsIsMissing() {
+        // given
+        Loan loan = loan();
+        JsonCommand command = makeJsonCommand("""
+                {
+                    "externalId": "12345",
+                    "dateFormat": "%s",
+                    "locale": "en",
+                    "startDate": "%s",
+                    "frequencyType": "MONTHS",
+                    "frequencyNumber": 1
+                }
+                """.formatted(DATE_FORMAT, formatDate(afterMaturity)));
+        // when
+        PlatformApiDataValidationException result = assertThrows(PlatformApiDataValidationException.class,
+                () -> underTest.validateReAge(loan, command));
+        // then
+        assertThat(result).isNotNull();
+        assertThat(result.getGlobalisationMessageCode()).isEqualTo("validation.msg.validation.errors.exist");
+        assertThat(result.getErrors().get(0).getUserMessageGlobalisationCode())
+                .isEqualTo("validation.msg.loan.reAge.numberOfInstallments.cannot.be.blank");
+    }
+
+    @Test
+    public void testValidateReAge_ShouldThrowException_WhenNumberOfInstallmentsIsZero() {
+        // given
+        Loan loan = loan();
+        JsonCommand command = makeJsonCommand("""
+                {
+                    "externalId": "12345",
+                    "dateFormat": "%s",
+                    "locale": "en",
+                    "startDate": "%s",
+                    "frequencyType": "MONTHS",
+                    "frequencyNumber": 1,
+                    "numberOfInstallments": 0
+                }
+                """.formatted(DATE_FORMAT, formatDate(afterMaturity)));
+        // when
+        PlatformApiDataValidationException result = assertThrows(PlatformApiDataValidationException.class,
+                () -> underTest.validateReAge(loan, command));
+        // then
+        assertThat(result).isNotNull();
+        assertThat(result.getGlobalisationMessageCode()).isEqualTo("validation.msg.validation.errors.exist");
+        assertThat(result.getErrors().get(0).getUserMessageGlobalisationCode())
+                .isEqualTo("validation.msg.loan.reAge.numberOfInstallments.not.greater.than.zero");
+    }
+
+    @Test
+    public void testValidateReAge_ShouldThrowException_WhenNumberOfInstallmentsIsNegative() {
+        // given
+        Loan loan = loan();
+        JsonCommand command = makeJsonCommand("""
+                {
+                    "externalId": "12345",
+                    "dateFormat": "%s",
+                    "locale": "en",
+                    "startDate": "%s",
+                    "frequencyType": "MONTHS",
+                    "frequencyNumber": 1,
+                    "numberOfInstallments": -1
+                }
+                """.formatted(DATE_FORMAT, formatDate(afterMaturity)));
+        // when
+        PlatformApiDataValidationException result = assertThrows(PlatformApiDataValidationException.class,
+                () -> underTest.validateReAge(loan, command));
+        // then
+        assertThat(result).isNotNull();
+        assertThat(result.getGlobalisationMessageCode()).isEqualTo("validation.msg.validation.errors.exist");
+        assertThat(result.getErrors().get(0).getUserMessageGlobalisationCode())
+                .isEqualTo("validation.msg.loan.reAge.numberOfInstallments.not.greater.than.zero");
+    }
+
+    @Test
+    public void testValidateReAge_ShouldThrowException_WhenLoanIsBeforeMaturity() {
+        // given
+        ThreadLocalContextUtil.setBusinessDates(new HashMap<>(Map.of(BusinessDateType.BUSINESS_DATE, actualDate)));
+        Loan loan = loan();
+        JsonCommand command = jsonCommand();
+        // when
+        GeneralPlatformDomainRuleException result = assertThrows(GeneralPlatformDomainRuleException.class,
+                () -> underTest.validateReAge(loan, command));
+        // then
+        assertThat(result).isNotNull();
+        assertThat(result.getGlobalisationMessageCode()).isEqualTo("error.msg.loan.reage.cannot.be.submitted.before.maturity");
+    }
+
+    @Test
+    public void testValidateReAge_ShouldThrowException_WhenStartDateIsBeforeMaturity() {
+        // given
+        Loan loan = loan();
+        given(loan.getMaturityDate()).willReturn(maturityDate);
+        String formattedDate = formatDate(maturityDate.minusDays(1));
+        JsonCommand command = jsonCommand("123456", formattedDate);
+        // when
+        PlatformApiDataValidationException result = assertThrows(PlatformApiDataValidationException.class,
+                () -> underTest.validateReAge(loan, command));
+        // then
+        assertThat(result).isNotNull();
+        assertThat(result.getGlobalisationMessageCode()).isEqualTo("validation.msg.validation.errors.exist");
+        assertThat(result.getErrors().get(0).getUserMessageGlobalisationCode())
+                .isEqualTo("validation.msg.loan.reAge.startDate.is.less.than.date");
+    }
+
+    @Test
+    public void testValidateReAge_ShouldThrowException_WhenLoanIsOnCumulativeSchedule() {
+        // given
+        Loan loan = loan();
+        given(loan.getLoanProductRelatedDetail().getLoanScheduleType()).willReturn(LoanScheduleType.CUMULATIVE);
+        JsonCommand command = jsonCommand();
+        // when
+        GeneralPlatformDomainRuleException result = assertThrows(GeneralPlatformDomainRuleException.class,
+                () -> underTest.validateReAge(loan, command));
+        // then
+        assertThat(result).isNotNull();
+        assertThat(result.getGlobalisationMessageCode())
+                .isEqualTo("error.msg.loan.reage.supported.only.for.progressive.loan.schedule.type");
+    }
+
+    @Test
+    public void testValidateReAge_ShouldThrowException_WhenLoanIsNotOnAdvancedPaymentAllocation() {
+        // given
+        Loan loan = loan();
+        given(loan.getTransactionProcessingStrategyCode())
+                .willReturn(DuePenFeeIntPriInAdvancePriPenFeeIntLoanRepaymentScheduleTransactionProcessor.STRATEGY_CODE);
+        JsonCommand command = jsonCommand();
+        // when
+        GeneralPlatformDomainRuleException result = assertThrows(GeneralPlatformDomainRuleException.class,
+                () -> underTest.validateReAge(loan, command));
+        // then
+        assertThat(result).isNotNull();
+        assertThat(result.getGlobalisationMessageCode())
+                .isEqualTo("error.msg.loan.reage.supported.only.for.progressive.loan.schedule.type");
+    }
+
+    @Test
+    public void testValidateReAge_ShouldThrowException_WhenLoanIsInterestBearing() {
+        // given
+        Loan loan = loan();
+        given(loan.isInterestBearing()).willReturn(true);
+        JsonCommand command = jsonCommand();
+        // when
+        GeneralPlatformDomainRuleException result = assertThrows(GeneralPlatformDomainRuleException.class,
+                () -> underTest.validateReAge(loan, command));
+        // then
+        assertThat(result).isNotNull();
+        assertThat(result.getGlobalisationMessageCode()).isEqualTo("error.msg.loan.reage.supported.only.for.non.interest.loans");
+    }
+
+    @Test
+    public void testValidateReAge_ShouldThrowException_WhenLoanIsNotActive() {
+        // given
+        Loan loan = loan();
+        given(loan.getStatus()).willReturn(LoanStatus.APPROVED);
+        JsonCommand command = jsonCommand();
+        // when
+        GeneralPlatformDomainRuleException result = assertThrows(GeneralPlatformDomainRuleException.class,
+                () -> underTest.validateReAge(loan, command));
+        // then
+        assertThat(result).isNotNull();
+        assertThat(result.getGlobalisationMessageCode()).isEqualTo("error.msg.loan.reage.supported.only.for.active.loans");
+    }
+
+    @Test
+    public void testValidateReAge_ShouldThrowException_WhenLoanAlreadyHasReAgeForToday() {
+        // given
+        List<LoanTransaction> transactions = List.of(loanTransaction(LoanTransactionType.DISBURSEMENT, maturityDate.minusDays(2)),
+                loanTransaction(LoanTransactionType.REAGE, businessDate));
+        Loan loan = loan();
+        given(loan.getLoanTransactions()).willReturn(transactions);
+        JsonCommand command = jsonCommand();
+        // when
+        GeneralPlatformDomainRuleException result = assertThrows(GeneralPlatformDomainRuleException.class,
+                () -> underTest.validateReAge(loan, command));
+        // then
+        assertThat(result).isNotNull();
+        assertThat(result.getGlobalisationMessageCode()).isEqualTo("error.msg.loan.reage.reage.transaction.already.present.for.today");
+    }
+
+    @Test
+    public void testValidateUndoReAge_ShouldThrowException_WhenLoanDoesntHaveReAge() {
+        // given
+        List<LoanTransaction> transactions = List.of(loanTransaction(LoanTransactionType.DISBURSEMENT, actualDate.minusDays(3)));
+        Loan loan = loan();
+        given(loan.getLoanTransactions()).willReturn(transactions);
+        JsonCommand command = jsonCommand();
+        // when
+        GeneralPlatformDomainRuleException result = assertThrows(GeneralPlatformDomainRuleException.class,
+                () -> underTest.validateUndoReAge(loan, command));
+        // then
+        assertThat(result).isNotNull();
+        assertThat(result.getGlobalisationMessageCode()).isEqualTo("error.msg.loan.reage.reaging.transaction.missing");
+    }
+
+    @Test
+    public void testValidateUndoReAge_ShouldThrowException_WhenLoanAlreadyHasRepaymentAfterReAge() {
+        // given
+        List<LoanTransaction> transactions = List.of(loanTransaction(LoanTransactionType.DISBURSEMENT, actualDate.minusDays(3)),
+                loanTransaction(LoanTransactionType.REAGE, actualDate.minusDays(2)),
+                loanTransaction(LoanTransactionType.REPAYMENT, actualDate.minusDays(1)));
+        Loan loan = loan();
+        given(loan.getLoanTransactions()).willReturn(transactions);
+        JsonCommand command = jsonCommand();
+        // when
+        GeneralPlatformDomainRuleException result = assertThrows(GeneralPlatformDomainRuleException.class,
+                () -> underTest.validateUndoReAge(loan, command));
+        // then
+        assertThat(result).isNotNull();
+        assertThat(result.getGlobalisationMessageCode()).isEqualTo("error.msg.loan.reage.repayment.exists.after.reaging");
+    }
+
+    @Test
+    public void testValidateUndoReAge_ShouldThrowException_WhenLoanAlreadyHasRepaymentAfterReAge_SameDay() {
+        // given
+        List<LoanTransaction> transactions = List.of(loanTransaction(LoanTransactionType.DISBURSEMENT, actualDate.minusDays(2)),
+                loanTransaction(LoanTransactionType.REAGE, actualDate.minusDays(1),
+                        OffsetDateTime.of(actualDate, LocalTime.of(10, 0), ZoneOffset.UTC)),
+                loanTransaction(LoanTransactionType.REPAYMENT, actualDate.minusDays(1),
+                        OffsetDateTime.of(actualDate, LocalTime.of(11, 0), ZoneOffset.UTC)));
+        Loan loan = loan();
+        given(loan.getLoanTransactions()).willReturn(transactions);
+        JsonCommand command = jsonCommand();
+        // when
+        GeneralPlatformDomainRuleException result = assertThrows(GeneralPlatformDomainRuleException.class,
+                () -> underTest.validateUndoReAge(loan, command));
+        // then
+        assertThat(result).isNotNull();
+        assertThat(result.getGlobalisationMessageCode()).isEqualTo("error.msg.loan.reage.repayment.exists.after.reaging");
+    }
+
+    @Test
+    public void testValidateUndoReAge_ShouldNotThrowException_WhenLoanAlreadyHasRepaymentAfterReAge_SameDay_RepaymentBeforeReAge() {
+        // given
+        List<LoanTransaction> transactions = List.of(loanTransaction(LoanTransactionType.DISBURSEMENT, actualDate.minusDays(2)),
+                loanTransaction(LoanTransactionType.REAGE, actualDate.minusDays(1),
+                        OffsetDateTime.of(actualDate, LocalTime.of(10, 0), ZoneOffset.UTC)),
+                loanTransaction(LoanTransactionType.REPAYMENT, actualDate.minusDays(1),
+                        OffsetDateTime.of(actualDate, LocalTime.of(9, 0), ZoneOffset.UTC)));
+        Loan loan = loan();
+        given(loan.getLoanTransactions()).willReturn(transactions);
+        JsonCommand command = jsonCommand();
+        // when
+        underTest.validateUndoReAge(loan, command);
+        // then no exception thrown
+    }
+
+    private JsonCommand jsonCommand() {
+        return jsonCommand("123456");
+    }
+
+    private JsonCommand jsonCommand(String externalId) {
+        return jsonCommand(externalId, formatDate(afterMaturity));
+    }
+
+    private String formatDate(LocalDate date) {
+        return DateTimeFormatter.ofPattern(DATE_FORMAT).format(date);
+    }
+
+    private JsonCommand jsonCommand(String externalId, String startDate) {
+        String json = """
+                {
+                    "externalId": "%s",
+                    "dateFormat": "%s",
+                    "locale": "en",
+                    "frequencyType": "MONTHS",
+                    "frequencyNumber": 1,
+                    "startDate": "%s",
+                    "numberOfInstallments": 1
+                }
+                """.formatted(externalId, DATE_FORMAT, startDate);
+        return makeJsonCommand(json);
+    }
+
+    private JsonCommand makeJsonCommand(String json) {
+        FromJsonHelper fromJsonHelper = new FromJsonHelper();
+        return new JsonCommand(1L, fromJsonHelper.parse(json), fromJsonHelper);
+    }
+
+    private LoanTransaction loanTransaction(LoanTransactionType type, LocalDate txDate, OffsetDateTime creationTime) {
+        LoanTransaction loanTransaction = loanTransaction(type, txDate);
+        given(loanTransaction.getCreatedDateTime()).willReturn(creationTime);
+        return loanTransaction;
+    }
+
+    private LoanTransaction loanTransaction(LoanTransactionType type, LocalDate txDate) {
+        LoanTransaction loanTransaction = mock(LoanTransaction.class);
+        given(loanTransaction.getTypeOf()).willReturn(type);
+        given(loanTransaction.getTransactionDate()).willReturn(txDate);
+        given(loanTransaction.getSubmittedOnDate()).willReturn(txDate);
+        return loanTransaction;
+    }
+
+    private Loan loan() {
+        Loan loan = mock(Loan.class);
+        given(loan.getStatus()).willReturn(LoanStatus.ACTIVE);
+        given(loan.getMaturityDate()).willReturn(maturityDate);
+        given(loan.getTransactionProcessingStrategyCode())
+                .willReturn(AdvancedPaymentScheduleTransactionProcessor.ADVANCED_PAYMENT_ALLOCATION_STRATEGY);
+        LoanProductRelatedDetail loanProductRelatedDetail = mock(LoanProductRelatedDetail.class);
+        given(loan.getLoanProductRelatedDetail()).willReturn(loanProductRelatedDetail);
+        given(loanProductRelatedDetail.getLoanScheduleType()).willReturn(LoanScheduleType.PROGRESSIVE);
+        given(loan.isInterestBearing()).willReturn(false);
+        given(loan.getLoanTransactions()).willReturn(List.of());
+        return loan;
+    }
+
+}