Can’t download free app

Basically to make use of the App Store and iTunes Store services you need a valid payment method on your Apple ID, unless you made the Apple ID in a very specific way.

It will ask for one until you add one and it can be verified. At that point, it can be safely removed, and won't ask for it again.

Easiest thing to do, is to just add one, and then remove it.

See here: link-> Create or use an Apple ID without a payment method - Apple Support

Do note that to verify the payment method, Apple may place an authorization hold on it. It should be reversed in a few days though.

See here: link->How apps, content, and subscriptions from Apple are billed - Apple Support

If the free app offers in app purchases you need a payment method.