code: public function sendHeaders()
      {
          if (php_sapi_name() !== "cli" && headers_sent($file, $line)) {
              throw new Exception("Try to send headers but headers already sent, output started at $file line $line.");
          }
  
          http_response_code($this->statusCode);
  
          foreach ($this->headers as $header) {
              if (php_sapi_name() !== "cli") {
                  header($header);
              }
          }
  
          return $this;
      }
docs: Send headers.
  
  @return self