PhantomJSCloud Error: Invalid Character ‘u’ – Python

I use PhantomJSCloud to take screenshots of web apps. While writing new code, I noticed this error coming back from the server:

   "message":"Error extracting userRequest. innerException: JSON5: invalid character 'u' at 1:1",
      "no stack unless env is DEV or TEST, or logLevel is DEBUG or TRACE"

The problem came because the request wasn’t JSON-encoding the object; the fix looks like this (using the requests library):

    post_data_string = json.dumps(python_object_here, sort_keys=True, indent=3, separators=(',', ': '))
    r ='', data=post_data_string)