code: protected function prepareRequestData()
      {
          // if POST or PUT, add parameters to post data, else add to uri
          if (in_array($this->command->getMethod(), ['POST', 'PUT'])) {
              $this->requestBody = $this->command->getEncodedData();
              $this->options[CURLOPT_POSTFIELDS] = $this->requestBody;
          }
  
          return $this;
      }
docs: Prepare request data
  
  @return $this