NotWhitelistedError(CUSTOMER_NOT_WHITELISTED_FOR_API) while uploading offline data using google AdWords API

I am new to Google Adwords. I have completed all initial configuration and integration required to use Adwords API. I have a test client account and I am able to get campaigns from that account. I also completed uploading offline data integration.

 // Upload offline data on the server and print some information.     OfflineDataUploadReturnValue returnValue =         offlineDataUploadService.mutate(operations.toArray(new OfflineDataUploadOperation[0]));     offlineDataUpload = returnValue.getValue(0);     System.out.printf(     "Uploaded offline data with external upload ID %d, and upload status %s.%n",     offlineDataUpload.getExternalUploadId(), offlineDataUpload.getUploadStatus()); 

But when I run the code to upload the data, I am facing below error:-

Request failed due to ApiException. Underlying ApiErrors:   Error 0: NotWhitelistedError{apiErrorType=NotWhitelistedError, errorString=NotWhitelistedError.CUSTOMER_NOT_WHITELISTED_FOR_API, fieldPath=, reason=CUSTOMER_NOT_WHITELISTED_FOR_API, trigger=} 

As I said earlier I am new to the Google AdWords, so any suggestion and help will be gladly appreciated. Thank you in advance!