error on form test

im getting this error on testing the form with test details

Warning: mysql_query(): Access denied for user 'root'@'localhost' (using password: NO) in /home/think/public_html/wp/wp-content/plugins/stripe-frontend-registration/main.php on line 125

Warning: mysql_query(): A link to the server could not be established in /home/think/public_html/wp/wp-content/plugins/stripe-frontend-registration/main.php on line 125

Warning: mysql_num_rows() expects parameter 1 to be resource, boolean given in /home/think/public_html/wp/wp-content/plugins/stripe-frontend-registration/main.php on line 125
You can use this Username

https://ww.wp.xz.cn/plugins/stripe-frontend-registration/