Why can't i purchase tabs for my guild bank?

[Rhagkulone]

Hey guys, a friend and me started a guild bank yesterday and farmed the 100g for the first guild bank tab, but it wouldn't let me purchase it. I turned of Bagnon though. It let me click purchase but nothing happens after that.

What can i do about that? or is it not possible to get a bank tab?

Thanks in advance.

Edit: We're playing on Lordaeron

Edit 2: We found a workaround! I gave the GM to my friend and he could buy it!