The blank page means your country doesn't allow you to buy fraises for tfm by phone, its okay tho they might add it later but I am not sure ^^

Can you get me a screenshot for this?

According to their website, Allopass does offer sms services for Serbia. So I'm not quite sure why it doesn't work for TFM.

Same thing with Croatia. It's up on the list but I cannot buy via Allopass.