What is my billing address because I can’t purchase anything

This support article includes how to change a billing (and shipping) address as part of editing a payment method for your account -->

Add a payment method to your Apple ID - Apple Support

On an iPhone/iPad:

1. Open the Settings app.

2. Tap your name.

3. Tap Payment & Shipping. You might be asked to sign in with your Apple ID.

4. To update the address for a payment method, tap the payment method, then edit your information. Tapping the method should reveal details for that method including the billing address. You might need to enter the security code that's printed on your credit or debit card. If you see Apple Pay after the last 4 digits of the card number, go to the Wallet app to edit the card information.

5. Edit the method then tap Done

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