Heda I also think there’s more to it than just the numbers. However, can’t the customer service add it for you anyway...? They know about it, they can see you’re from Germany, why not add it for you or approve it?
I had no problems adding my bunq card btw, but I’m cancelling the service again. It’s absolutely horrible, I’ll wait for them to sort the issues out first and wait for them to add AirPlay support or release a tvOS app.