Blog Comments – Fatal error: Uncaught Error: Call to undefined function

Hello. I’m using WordPress 4.8 and have noticed the following error whenever anyone (including myself as admin) leaves a comment on my blog:

Fatal error: Uncaught Error: Call to undefined function mysql_escape_string() in /home/thedi198/public_html/wp-content/plugins/comment-reply-notification/comment-reply-notification.php:113 Stack trace: #0 /home/thedi198/public_html/wp-includes/class-wp-hook.php(300): comment_reply_notification->email(287) #1 /home/thedi198/public_html/wp-includes/class-wp-hook.php(323): WP_Hook->apply_filters(287, Array) #2 /home/thedi198/public_html/wp-includes/plugin.php(453): WP_Hook->do_action(Array) #3 /home/thedi198/public_html/wp-includes/comment.php(1981): do_action('comment_post', 287, 1, Array) #4 /home/thedi198/public_html/wp-includes/comment.php(3095): wp_new_comment(Array, true) #5 /home/thedi198/public_html/wp-comments-post.php(25): wp_handle_comment_submission(Array) #6 {main} thrown in /home/thedi198/public_html/wp-content/plugins/comment-reply-notification/comment-reply-notification.php on line 113

The comment is still successful but after hitting submit, a white screen with the error above appears. Upon refreshing the page and going back to view the comments, the new comment is there without any problem, which is good I suppose.

But this is a problem I could be doing without. I thought it may have been the child theme but this issue actually existing before I switched theme and created the child.

Anyone able to help me solve the problem? Help would be much appreciated!

The site is https://www.thedigitalcrusader.com and is self-hosted with GoDaddy & SiteGround. (URL & WebHost respectively)

Many thanks,

CJ