GG Did you try at one of the supported gas stations or at some small shop? At least my experience in Germany (when paying for other stuff via Paysafe) was that at gas stations the staff often knows how to search for the right card, but the smaller shops sometimes don't.
I don't know the ins and outs of how it works behind the scenes, but these smaller shops probably buy some kind of package that enables them to sell a bunch of different prepaid cards including Paysafecash, but because the demand is low the staff don't actually know how to sell every type of card, only the most common ones.