Online payment with foreign credit card / paypal in usa

You can probably use your credit card in an Apple store. If you want to buy online from Apple.com you must either ask for in-store pickup or provide a delivery address in the US, and it might accept your credit card. Two things to be aware of:

1. An iPhone 14 bought in the US will have eSIM only, no slot for a physical SIM. I checked, and there are only 2 carriers in Belgium that can use eSIM: Orange and Ubigi.
2. iPhone warranties are not international. If the phone ever needs repair by Apple it will have to be returned to the US.

Well, the general answer to “why” is that Apple won’t let you. Specifically, because what is available in the app store is region and country-specific to comply with local laws and copyright, so you must reside in the country of the iTunes & App Store that you are connected to. They use the billing address of the credit card to verify.

Based on your country of residence and country you have selected under your Apple ID --> Payment methods that you can use with your Apple ID - Apple ...

No. The billing address and credit card address must match your Apple ID address.