Can’t edit the Thank You For Your Order Page

Hello team,

Thank you so much for this amazing plugin. It was working perfectly when I bought it, but am having trouble with it now.

I can’t edit the Thank You For Your Order Page. Whenever I try to design Thank You Page it gives me this error :

There has been a critical error on your website.

Learn more about debugging in WordPress.

Please help me solve this problem, Thank you.