diff --git a/apps/onboarding-ms/src/main/java/it/pagopa/selfcare/onboarding/controller/OnboardingController.java b/apps/onboarding-ms/src/main/java/it/pagopa/selfcare/onboarding/controller/OnboardingController.java
index ad15324ac..a4cd07668 100644
--- a/apps/onboarding-ms/src/main/java/it/pagopa/selfcare/onboarding/controller/OnboardingController.java
+++ b/apps/onboarding-ms/src/main/java/it/pagopa/selfcare/onboarding/controller/OnboardingController.java
@@ -134,10 +134,12 @@ public Uni<OnboardingGetResponse> getOnboardingWithFilter(@QueryParam(value = "p
         return onboardingService.onboardingGet(productId, taxCode, status, from, to, page, size);
     }
 
+    @Operation(summary = "Perform reject operation of an onboarding request receiving onboarding id." +
+            "Function change status to REJECT for an onboarding request that is not COMPLETED. " )
     @PUT
-    @Path("/{onboardingId}/delete")
+    @Path("/{onboardingId}/reject")
     public Uni<Response> delete(@PathParam(value = "onboardingId") String onboardingId) {
-        return onboardingService.deleteOnboarding(onboardingId)
+        return onboardingService.rejectOnboarding(onboardingId)
                 .map(ignore -> Response
                         .status(HttpStatus.SC_NO_CONTENT)
                         .build());
diff --git a/apps/onboarding-ms/src/main/java/it/pagopa/selfcare/onboarding/service/OnboardingService.java b/apps/onboarding-ms/src/main/java/it/pagopa/selfcare/onboarding/service/OnboardingService.java
index 18ff9afc7..96ff3ca4a 100644
--- a/apps/onboarding-ms/src/main/java/it/pagopa/selfcare/onboarding/service/OnboardingService.java
+++ b/apps/onboarding-ms/src/main/java/it/pagopa/selfcare/onboarding/service/OnboardingService.java
@@ -28,7 +28,7 @@ public interface OnboardingService {
 
     Uni<OnboardingGetResponse> onboardingGet(String productId, String taxCode, String status, String from, String to, Integer page, Integer size);
 
-    Uni<Long> deleteOnboarding(String onboardingId);
+    Uni<Long> rejectOnboarding(String onboardingId);
 
     Uni<OnboardingGet> onboardingPending(String onboardingId);
 
diff --git a/apps/onboarding-ms/src/main/java/it/pagopa/selfcare/onboarding/service/OnboardingServiceDefault.java b/apps/onboarding-ms/src/main/java/it/pagopa/selfcare/onboarding/service/OnboardingServiceDefault.java
index 44baaf67a..02b297aa9 100644
--- a/apps/onboarding-ms/src/main/java/it/pagopa/selfcare/onboarding/service/OnboardingServiceDefault.java
+++ b/apps/onboarding-ms/src/main/java/it/pagopa/selfcare/onboarding/service/OnboardingServiceDefault.java
@@ -557,10 +557,14 @@ private List<OnboardingGet> convertOnboardingListToResponse(List<Onboarding> ite
     }
 
     @Override
-    public Uni<Long> deleteOnboarding(String onboardingId) {
+    public Uni<Long> rejectOnboarding(String onboardingId) {
         return checkOnboardingIdFormat(onboardingId)
-                .onItem()
-                .transformToUni(id -> updateStatus(onboardingId, OnboardingStatus.DELETED));
+                .onItem().transformToUni(ignore -> Onboarding.findById(new ObjectId(onboardingId))
+                        .onItem().transform(onboarding -> (Onboarding) onboarding))
+                .onItem().transformToUni(onboardingGet -> OnboardingStatus.COMPLETED.equals(onboardingGet.getStatus())
+                        ? Uni.createFrom().failure(new InvalidRequestException(String.format("Onboarding with id %s is COMPLETED!", onboardingId)))
+                        : Uni.createFrom().item(onboardingGet))
+                .onItem().transformToUni(id -> updateStatus(onboardingId, OnboardingStatus.REJECTED));
     }
 
     /**
diff --git a/apps/onboarding-ms/src/test/java/it/pagopa/selfcare/onboarding/controller/OnboardingControllerTest.java b/apps/onboarding-ms/src/test/java/it/pagopa/selfcare/onboarding/controller/OnboardingControllerTest.java
index 42288e018..5da7a2305 100644
--- a/apps/onboarding-ms/src/test/java/it/pagopa/selfcare/onboarding/controller/OnboardingControllerTest.java
+++ b/apps/onboarding-ms/src/test/java/it/pagopa/selfcare/onboarding/controller/OnboardingControllerTest.java
@@ -232,19 +232,19 @@ void complete() throws IOException {
     void deleteOK(){
         String onboardingId = "actual-onboarding-id";
 
-        when(onboardingService.deleteOnboarding(onboardingId))
+        when(onboardingService.rejectOnboarding(onboardingId))
                 .thenReturn(Uni.createFrom().item(1L));
 
         given()
                 .when()
                 .pathParam("onboardingId", onboardingId)
-                .put("/{onboardingId}/delete")
+                .put("/{onboardingId}/reject")
                 .then()
                 .statusCode(204);
 
         ArgumentCaptor<String> expectedId = ArgumentCaptor.forClass(String.class);
         verify(onboardingService, times(1))
-                .deleteOnboarding(expectedId.capture());
+                .rejectOnboarding(expectedId.capture());
         assertEquals(expectedId.getValue(), onboardingId);
     }
 
@@ -253,19 +253,19 @@ void deleteOK(){
     void deleteInvalidOnboardingIdOrOnboardingNotFound(){
         String onboardingId = "actual-onboarding-id";
 
-        when(onboardingService.deleteOnboarding(onboardingId))
+        when(onboardingService.rejectOnboarding(onboardingId))
                 .thenThrow(InvalidRequestException.class);
 
         given()
                 .when()
                 .pathParam("onboardingId", onboardingId)
-                .put("/{onboardingId}/delete")
+                .put("/{onboardingId}/reject")
                 .then()
                 .statusCode(400);
 
         ArgumentCaptor<String> expectedId = ArgumentCaptor.forClass(String.class);
         verify(onboardingService, times(1))
-                .deleteOnboarding(expectedId.capture());
+                .rejectOnboarding(expectedId.capture());
         assertEquals(expectedId.getValue(), onboardingId);
     }
 
diff --git a/apps/onboarding-ms/src/test/java/it/pagopa/selfcare/onboarding/service/OnboardingServiceDefaultTest.java b/apps/onboarding-ms/src/test/java/it/pagopa/selfcare/onboarding/service/OnboardingServiceDefaultTest.java
index 7cae44fd1..990145e67 100644
--- a/apps/onboarding-ms/src/test/java/it/pagopa/selfcare/onboarding/service/OnboardingServiceDefaultTest.java
+++ b/apps/onboarding-ms/src/test/java/it/pagopa/selfcare/onboarding/service/OnboardingServiceDefaultTest.java
@@ -1003,10 +1003,15 @@ private Onboarding createDummyOnboarding() {
 
     @Test
     void testOnboardingUpdateStatusOK() {
-        String onboardingId = "655df045dc52ea5f37c80955";
-        mockUpdateOnboarding(onboardingId, 1L);
+
+        Onboarding onboarding = createDummyOnboarding();
+        PanacheMock.mock(Onboarding.class);
+        when(Onboarding.findById(onboarding.getId()))
+                .thenReturn(Uni.createFrom().item(onboarding));
+
+        mockUpdateOnboarding(onboarding.getId().toHexString(), 1L);
         UniAssertSubscriber<Long> subscriber = onboardingService
-                .deleteOnboarding(onboardingId)
+                .rejectOnboarding(onboarding.getId().toHexString())
                 .subscribe()
                 .withSubscriber(UniAssertSubscriber.create());
 
@@ -1017,29 +1022,51 @@ void testOnboardingUpdateStatusOK() {
     void testOnboardingUpdateStatusInvalidOnboardingId() {
         String onboardingId = "123456";
         UniAssertSubscriber<Long> subscriber = onboardingService
-                .deleteOnboarding(onboardingId)
+                .rejectOnboarding(onboardingId)
                 .subscribe()
                 .withSubscriber(UniAssertSubscriber.create());
 
         subscriber.assertFailedWith(InvalidRequestException.class, "Given onboardingId [123456] has wrong format");
     }
 
+    @Test
+    void rejectOnboarding_statusIsCOMPLETED() {
+        Onboarding onboarding = createDummyOnboarding();
+        onboarding.setStatus(OnboardingStatus.COMPLETED);
+        PanacheMock.mock(Onboarding.class);
+        when(Onboarding.findById(onboarding.getId()))
+                .thenReturn(Uni.createFrom().item(onboarding));
+
+        mockUpdateOnboarding(onboarding.getId().toHexString(), 1L);
+        UniAssertSubscriber<Long> subscriber = onboardingService
+                .rejectOnboarding(onboarding.getId().toHexString())
+                .subscribe()
+                .withSubscriber(UniAssertSubscriber.create());
+
+        subscriber.assertFailedWith(InvalidRequestException.class);
+    }
+
     @Test
     void testOnboardingDeleteOnboardingNotFoundOrAlreadyDeleted() {
-        String onboardingId = "655df045dc52ea5f37c80955";
-        mockUpdateOnboarding(onboardingId, 0L);
+
+        Onboarding onboarding = createDummyOnboarding();
+        PanacheMock.mock(Onboarding.class);
+        when(Onboarding.findById(onboarding.getId()))
+                .thenReturn(Uni.createFrom().item(onboarding));
+        mockUpdateOnboarding(onboarding.getId().toHexString(), 0L);
+
         UniAssertSubscriber<Long> subscriber = onboardingService
-                .deleteOnboarding(onboardingId)
+                .rejectOnboarding(onboarding.getId().toHexString())
                 .subscribe()
                 .withSubscriber(UniAssertSubscriber.create());
 
-        subscriber.assertFailedWith(InvalidRequestException.class, "Onboarding with id 655df045dc52ea5f37c80955 not found or already deleted");
+        subscriber.assertFailedWith(InvalidRequestException.class);
     }
 
     private void mockUpdateOnboarding(String onboardingId, Long updatedItemCount) {
         ReactivePanacheUpdate query = mock(ReactivePanacheUpdate.class);
         PanacheMock.mock(Onboarding.class);
-        when(Onboarding.update(Onboarding.Fields.status.name(), OnboardingStatus.DELETED)).thenReturn(query);
+        when(Onboarding.update(Onboarding.Fields.status.name(), OnboardingStatus.REJECTED)).thenReturn(query);
         when(query.where("_id", onboardingId)).thenReturn(Uni.createFrom().item(updatedItemCount));
     }