I can’t remove my payment method

It is not possible, you may need to have a payment method on file, even if the app you want to download is free.

If you don't want to use your bank card, you can also use your Apple ID balance as payment method:

Add money to your Apple ID balance

Add money to your Apple ID balance – Apple Support (UK)

See the Apple Support article(s) below. Link to contact Apple Support is at the end of the article.

Apple ID - If you can't remove your last payment method or use no payment method with your Apple ID