I had another user with the same problem earlier but so far I do not have a solution either.
I don't have any additional information atm either, as per the official announcements these cards will still be *sold* the next 2 weeks, and all cards that have been sold until then should function until September 30.
A quick google search for the error message posted seems to hint that it is a common problem on PayByCashs end which seems to be the payment processor for that.