Warning: require(vendor/autoload.php): failed to open stream: No such file or directory in /opt/lampp/htdocs/plugin/PHPMailer/get_oauth_token.php on line 18

Fatal error: require(): Failed opening required 'vendor/autoload.php' (include_path='.:/opt/lampp/lib/php') in /opt/lampp/htdocs/plugin/PHPMailer/get_oauth_token.php on line 18