Unable to make in-game purchase with Apple Account balance in Diablo Immortal

I want to make an in-game purchase in Diablo Immortal, but it says it’s not possible and that I need to contact iTunes support. What could be the reason and how can I fix it? I’m paying with my Apple account balance, which I topped up using a gift card, and there are sufficient funds.

[Re-Titled by Moderator]

Original Title: Game