Api error when trying to Get/Downlaod a document

[lotfio]

Hello there,
We are trying to integrate signNow. we were able to upload a template pdf generate documents from the template & create signing links. However when trying to get/download a signed document we are getting some response errors

the ssue seems to be related to the response manager as we can see the response showing fine at guzzle http but when it reaches signNow response manager (validate & map) it throws the error

we are also suspecting it related to the custom added fields to the template. here is an example of a field we are adding:

  // 2. Add fields to the document
  $fields = new FieldCollection();
  $fields->add(
      new Field(
          x: 100,
          y: 640,
          width: 200,
          height: 100,
          type: 'signature',
          pageNumber: 0,
          required: true,
          role: 'Linguist',
          name: 'signature_field',
          label: 'Signature',
      )
  );

  $request = new DocumentPut(
      fields: $fields,
  );
  $request->withDocumentId($response->getId());
  $response = $apiClient->send($request);

Any suggestions or help is mutch appreciated ?
Thank you
@JiSoft