I assume it's a region locked situation. Most cards usually require your current location to generally be the same region you're purchasing for (for example: to buy an EU subscription, you must physically be in the EU since the subscription bills from within the EU). Not all cards will do this, but in general most cards will do this. If you're actually buying the game and upgrading from the trial, then this is even more likely the case. If you already bought the game, it's probably easiest to just buy a time card if you're have issues.