@_peteyg we replied to your support email, as the issue has been resolved. Please see the details there.
For everyone else, this was mainly due to a US ZIP code missing in our system, which is rare but does happen sometimes. If you have this issue, let us know and we'll get the ZIP code added!
For the credit card not being deleted, it was actually because @_peteyg was actually repeatedly adding copies of that payment method to the account when getting the ZIP code error, which is an edge case not really shown in our UI since our system is designed for a single default payment method, which is the latest one added. When the payment method was repeatedly being deleted, those copies were getting removed, there were about 3 left by the time I checked