Why can’t I use my Apple account to make in-app purchases?

First, can you tell me what country or region your Apple account is set to? Also, what's the name of the app you're trying to make purchases in? There are different types of in-app purchases (IAPs) that could affect this, like consumable or non-consumable items. Understanding these could help troubleshoot your issue better.

If you're in Italy and trying to buy content in Honkai: Star Rail, ensure your payment method and Apple account settings are correct. Sometimes, you might need to update your account information or check if there are regional restrictions.