After submitting and paying for a booking on FAT Booking system via PayPal, instead of being returned to the website with confirmation, users get the following error: There has been a critical error on your website. Please check your site admin email inbox for instructions. However the PayPal payment DOES go through AND the booking IS successful in the system. The only issue is the error message. This was working fine before and has only just started appearing so maybe a WordPress update is causing this or php issue?