code: private function buildRequestHeaders($body)
      {
          $headers = $this->getEbayHeaders();
  
          $headers['Accept'] = 'application/json';
          $headers['Content-Type'] = 'application/json';
          $headers['Content-Length'] = strlen($body);
  
          // Add optional headers.
          if ($this->getConfig('requestLanguage')) {
              $headers[self::HDR_REQUEST_LANGUAGE] = $this->getConfig('requestLanguage');
          }
  
          if ($this->getConfig('responseLanguage')) {
              $headers[self::HDR_RESPONSE_LANGUAGE] = $this->getConfig('responseLanguage');
          }
  
          if ($this->getConfig('compressResponse')) {
              $headers[self::HDR_RESPONSE_ENCODING] = 'application/gzip';
          }
  
          return $headers;
      }
docs: Helper function that builds the HTTP request headers.
  
  @param string $body The request body.
  
  @return array An associative array of HTTP headers.