Error Log: MathRank Plugin with Enfold Theme

Here’s the log error I’m getting. I’m not sure how to solve it.

[13-Aug-2021 19:03:00 UTC] PHP Warning: Use of undefined constant enfold_child_prepay_redirect - assumed ‘enfold_child_prepay_redirect’ (this will throw an Error in a future version of PHP) in /opt/wordpress/wp-content/themes/enfold-child/functions.php on line 453
[13-Aug-2021 19:03:00 UTC] PHP Warning: Use of undefined constant enfold_child_member_signup - assumed ‘enfold_child_member_signup’ (this will throw an Error in a future version of PHP) in /opt/wordpress/wp-content/themes/enfold-child/functions.php on line 486

It’s PHP version/compatibility issue