I have this method and tried everything but mocking is not working as expected

@Override
    public ClaimSubmissionResponse generateJsonFileProfessional(String claimType, String correlationId,
            String jsonContent, String authToken) {
        ClaimSubmissionResponse claimSubmissionResponse = new ClaimSubmissionResponse();
        try {
            if (isSelfServicePortalServerAvailable(selfServicePortalURL)) {
                HttpHeaders headers = populateTokenHeaders(authToken);
                String corelationId = UUID.randomUUID().toString();
                InetAddress ipAddress = InetAddress.getLocalHost();
                HttpEntity<String> request = new HttpEntity<>(jsonContent, headers);
                String claimSubmissionAPI = selfServicePortalURL + Endpoints.SUBMIT_CLAIM_PROFESSIONAL;
                processRequestAudit(jsonContent, corelationId, corelationId, ipAddress.toString(), "Generate Json File",
                        "Claim Submission");
                UriComponentsBuilder builder = UriComponentsBuilder.fromUriString(claimSubmissionAPI)
                        .queryParam("claimType", claimType).queryParam("correlationId", correlationId);
                ResponseEntity<ClaimSubmissionResponse> response = restTemplate.exchange(
                        builder.buildAndExpand().toUri(), HttpMethod.POST, request, ClaimSubmissionResponse.class);
                claimSubmissionResponse = response.getBody();
                processResponseAudit(claimSubmissionResponse, "", corelationId, corelationId);
            } else {
                log.info(SELF_SERVICE_PORTAL_UNAVAILABLE_MESSAGE);
            }
        } catch (Exception cause) {
            log.error("The Error While Executing the API Call :: {} ", cause.getMessage());
        }
        return claimSubmissionResponse;
    }

junit test case

 @Test
public void testGenerateJsonFileProfessional_Success() throws Exception {
    // Mocking external methods and variables
    String claimType = "type1";
    String correlationId = UUID.randomUUID().toString();
    String jsonContent = "{}";
    String authToken = "token123";
    String corelationId = UUID.randomUUID().toString();
    InetAddress ipAddress = InetAddress.getLocalHost();
    // Mocking isSelfServicePortalServerAvailable
    when(selfServiceCoreClaimImpl.isSelfServicePortalServerAvailable(selfServicePortalURL)).thenReturn(true);
    // Mocking populateTokenHeaders
    when(selfServiceCoreClaimImpl.populateTokenHeaders(authToken)).thenReturn(httpHeaders);
    // Mocking RestTemplate response
    ClaimSubmissionResponse expectedResponse = new ClaimSubmissionResponse();
    ResponseEntity<ClaimSubmissionResponse> mockResponse = new ResponseEntity<>(expectedResponse, HttpStatus.OK);
    // UriComponentsBuilder mock setup
    UriComponentsBuilder builder = UriComponentsBuilder.fromUriString(selfServicePortalURL)
            .queryParam("claimType", claimType)
            .queryParam("correlationId", correlationId);
    when(restTemplateTest.exchange(
            builder.buildAndExpand().toUri(), HttpMethod.POST, new HttpEntity<>(jsonContent, httpHeaders), ClaimSubmissionResponse.class))
        .thenReturn(mockResponse);
    // Call the method under test
    ClaimSubmissionResponse actualResponse = selfServiceCoreClaimImpl.generateJsonFileProfessional(claimType, correlationId, jsonContent, authToken);
    // Assertions
    assertNotNull(actualResponse);
    assertEquals(expectedResponse, actualResponse);
    // Verify RestTemplate was called
    verify(restTemplateTest).exchange(
            builder.buildAndExpand().toUri(), HttpMethod.POST, new HttpEntity<>(jsonContent, httpHeaders), ClaimSubmissionResponse.class);
}

}

getting this eeror

org.mockito.exceptions.misusing.MissingMethodInvocationException:
when() requires an argument which has to be ‘a method call on a mock’.
For example:
when(mock.getArticles()).thenReturn(articles);

Also, this error might show up because:

1. you stub either of: final/private/equals()/hashCode() methods.
   Those methods cannot be stubbed/verified.
   Mocking methods declared on non-public parent classes is not supported.

2. inside when() you don’t call method on mock but on some other object.

   at com.acentra.ssp.impl.SelfServiceCoreClaimImplTest.testGenerateJsonFileProfessional_Success(SelfServiceCoreClaimImplTest.java:170)
   at java.base/java.lang.reflect.Method.invoke(Method.java:568)
   at java.base/java.util.ArrayList.forEach(ArrayList.java:1511)
   at java.base/java.util.ArrayList.forEach(ArrayList.java:1511)

Not sure where i am doing wrong. Thanks if someone can help. I stuck in this from past 2 days. tried everthing but not worked.

updated the test method to this :

 @Test
public void testGenerateJsonFile_Success() {
    ClaimSubmissionResponse mockResponse = new ClaimSubmissionResponse();
    ResponseEntity<ClaimSubmissionResponse> responseEntity = mock(ResponseEntity.class);
    when(responseEntity.getBody()).thenReturn(mockResponse);
    when(restTemplate.exchange(any(), eq(HttpMethod.POST), any(HttpEntity.class), eq(ClaimSubmissionResponse.class))).thenReturn(responseEntity);

    ClaimSubmissionResponse response = selfServiceCoreClaimImpl.generateJsonFileProfessional("claimType", "correlationId", "jsonContent", "testdata");
    assertNotNull(response);
}

then
response is getting null here

ResponseEntity<ClaimSubmissionResponse> response = restTemplate.exchange(
                        builder.buildAndExpand().toUri(), HttpMethod.POST, request, ClaimSubmissionResponse.class);
                claimSubmissionResponse = response.getBody();

error is

org.mockito.exceptions.misusing.UnnecessaryStubbingException:
Unnecessary stubbings detected.
Clean & maintainable test code requires zero unnecessary code.
Following stubbings are unnecessary (click to navigate to relevant line of code):

1. -> at com.impl.SelfServiceCoreClaimImplTest.testGenerateJsonFile_Success(SelfServiceCoreClaimImplTest.java:147)
2. -> at com.impl.SelfServiceCoreClaimImplTest.testGenerateJsonFile_Success(SelfServiceCoreClaimImplTest.java:148)
   Please remove unnecessary stubbings or use ‘lenient’ strictness. More info: javadoc for UnnecessaryStubbingException class.
   at org.mockito.junit.jupiter.MockitoExtension.afterEach(MockitoExtension.java:192)
   at java.base/java.util.ArrayList.forEach(ArrayList.java:1511)
   at java.base/java.util.ArrayList.forEach(ArrayList.java:1511)