Not able to create hosting accounts and client product page displays error

[KevvTheGoat]

WHMCS 8

On client page it says
Oops!
Something went wrong and we couldn't process your request.
Please go back to the previous page and try again.

It shows that it successfully created the hosting account but it didn't, and product page is inaccessible

[MS-DOS2]

Hello,

I had written this script for WHMCS 7, I can update it, can you tell me the exact error?
Enable error display in WHMCS settings and send me what you see.

[ahmadmahdizadehesfanjani]