I've updated the "Read first: Known issues, reporting a bug" thread with the explanation. Basically, this is what it says:
"Payment option down
PayByCash doesn't work: Since the company that owns PayByCash (or PBC) has been bought by another company, they have been in the process of rebranding for quite some time now. Their new name will be UltimatePay once they make it work for BB. We have prepared and tested the new system but they are having some issues or have just decided not to let it go public for BB. This is baffling for us since it will soon be almost a year.
So, as an alternative, we advise our users to use AdKnowledge SuperRewards instead. Actually, it's quite simple: buy Supporter points using their payment system and then use those to buy Supporter or the second team option. They even have bank transfer and cash options!"