I also had the same problem. I once read that there has to be enough money on the paypal account in order to make a different option show up. The option appeared but I still did not succeed in paying to Groundspeak.
At last, I sent the money to Groundspeak without the link on geocaching.com and wrote an email to contact@Groundspeak.com, following that guide (sorry, only in German, but the fourth screenshot might help).