Yes, it is a technical issue. eBay we are told are aware and working on it, that some buyers in European countries especially, aside from the long time issue with the States, are finding it impossible to pay after buying.
A seller reported this, which helped them.
Remove GSP from your site preferences and also deselect Evri as a postage option, only use Royal Mail (international), and that seemed to work.
Worth a try !
@jmc.autosalvage