How to POST Form data with multiple attachments using Retrofit

RestClient.java

    public interface FormUploadService {

     @Multipart
     @POST("<post-url-endpoint>") // the post url endpoint
     Observable < String > postFormWithAttachments(
      @Header(AppConstants.KEY_AUTH) String authKey, // auth key, if required
      @PartMap Map < String, RequestBody > params); // our form data map
    }

    public void postForm(String authKey,
     FormPostObject formPostObject,
     List < File > attachments,
     Callback < ResultObject > resultObjectCallback) {

     Map < String, RequestBody > map = new HashMap < > ();

     map.put("description", toRequestBody(formPostObject.getDescription()));
     map.put("subject", toRequestBody(formPostObject.getSubject()));
     map.put("email", toRequestBody(formPostObject.getEmail()));

     if (attachments != null && attachments.size() > 0) {
      for (int i = 0, size = attachments.size(); i < size; i++) {
       File file = attachments.get(i);
       RequestBody fileBody = RequestBody.create(MediaType.parse("multipart/form-data"), file);
       // replace the 'attachments[]' with your expected form data name
       map.put("form-data; name=\"attachments[]\"; filename=\"" + file.getName() + "\";", fileBody);
      }
     }

     formUploadService.postFormWithAttachments(authKey, map).enqueue(resultObjectCallback);
    }


    private RequestBody toRequestBody(String value) {
     RequestBody body = RequestBody.create(MediaType.parse("text/plain"), value);
     return body;
    }