Also, currently facing this Sandbox bug where the increased price on App Store Connect is not being reflected on the Apple payment sheet. Feedback filed here: https://feedbackassistant.apple.com/feedback/13225803

All works perfectly now, thanks.

Yes, I'm also experiencing the same error on multiple devices and accounts. One says "Unable to process your request. Try again later.", the other says "Your request couldn't be completed. Try again later." I've checked Apple System Status page and all seems fine with Sandbox. Edit: Feedback filed here FB17437891