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Fatal error: require(): Failed opening required 'vendor/autoload.php' (include_path='.:/opt/lampstack-5.6.29-0-tech/php/lib/php:/opt/lampstack-5.6.29-0-tech/frameworks/smarty/libs') in /opt/lampstack-5.6.29-0-tech/apache2/htdocs/plugin/PHPMailer/get_oauth_token.php on line 18