It's been reported that many club members are experiencing a 400 error page while trying to make payments on Club System sites. I have been investigating this issue, and have raised a support ticket with PayPal who have acknowledged that it is an issue with a redirect link within their process, which means unfortunately it is outside my control to resolve. I have been chasing them daily, and am waiting on an ETA for a resolution.
This issue seems to show only when you are logged into PayPal, so as a workaround members can log out of PayPal, and then try again choosing to Continue as Guest.
I know this is very bad timing, considering lots of clubs are getting subscriptions paid, and are opening bookings soon. I am doing everything I can to work with PayPal and get this resolved as fast as possible.
Note that Club System also offers integration with Stripe, which is a simplified process for users, as they enter their credit card details into a secure widget within the Club System site. It also seems to be more stable, based on the issues I've seen over the years with PayPal compared to Stripe.
Moving to Stripe would of course involve your club setting up a Stripe account as opposed to PayPal, but its a pretty straight forward process, so if you are interested in switching please reach out to discuss.