if you’re ever struggling with some web app that keeps giving you opaque failure messages when you try and do something that should just work, my tried and tested advice is
open the network inspector
like. a good 80% of the time. there’ll be a detailed reason (or enough info to infer one) in the actual responses from their backend.
plus you get to see fun things like "status": "FRAUD_DECLINE" rather than a message that just says “decwined :((( awa pwease contact us"