Let me share the issue you're having with buying connects with the team and they'll reach out to you directly via a support ticket to assist.
I can't add my debit Mastercard. It says, "We are unable to authorize your card. Please add another billing method or contact your issuing bank." I don't think there is anything wrong with my card.
Upwork seems to be having issues with its site currently. There are a few parts to the site that aren't working. I would try a different browser, or try again later.
I checked and, unfortunately, it looks like the charge was declined on the credit card. Please, contact your bank to check if your credit card is set up to be used for international purchases via the Internet.