Unable to add billing address with Irish postcode

When I try to add a billing id on the App Store on my MacBook, it won't accept my postcode. When I try to enter a postcode in the eircode format (i.e. "WW00X123") I'm given the following error message:

"postcode may be empty, or for Dublin, please enter a one-or-two-digit code, or a digit followed by a letter."

Of course I've tried various options, no postcode, a "one-or-two-digit code, or a digit followed by a letter", but in either case, I'm given an error message.

What's slightly irritating about this error message, it's that I've actually been experiencing the same error message for about four years now on different occasions. Using different postal addresses (I've moved house), different email addresses, but always the same error message.

I need to buy a new phone, and was thinking of getting an iPhone, but if I can't install apps, then that's a non-runner.