Had the same issue yesterday. I wanted to buy some stuff from the Shop but my card got rejected with the same error code.
Ended up using crypto instead (Litecoin). Something to mention here, the coins were not credited instantly as the description says. It took ~30 minutes after there were 6/6 confirmations for the transaction and only then did the coins appear in my account.
Just to keep this in mind if someone is donating via LTC.