code: protected function buildMultipartFormDataFilePayload($name, $attachment)
      {
          return sprintf(
              '%s%s%s%s%s',
              '--boundary'.self::CRLF,
              'Content-Disposition: form-data; name="'.$name.'"; filename="picture"'.self::CRLF,
              'Content-Type: '.$attachment['mimeType'].self::CRLF.self::CRLF,
              $attachment['data'].self::CRLF,
              '--boundary--'
          );
      }
docs: Builds the file part of a multipart/form-data request body.
  
  @param string $name
  @param array $attachment
  
  @return string The file part of a multipart/form-data request body.