WHMCS WP Integration is acting up when I try to finish the order (redirecting to wrong url)

Hello there,

So when I choose to "Pay" for selected package it redirects me to url.com/?whmcs instead of the url.com/client/?whmcs where it was originally supposed to be.

Until the last moment the address is at url.com/client/?whmcs, but when I click "Pay" it loses the /client/ and makes it show nothing.

Logically I could fix this, but I think its best for you guys to give me a tip what to do.

Yes, in the options I have chosen the default content page as the /client/ page I was talking about.

Awaiting for your feedback.

Best regards,