Why is Apple making me add a payment option for a free app

Are you subscribing to a free trial through whatever the app is you are trying to download?

You will need to have at least that much money in your Apple ID balance, to be able to buy an app.

If you don't want to choose a credit or banking card, you can also redeem an Apple Gift Card:

How to redeem your Apple Gift Card or App Store & iTunes gift card - Apple Support