Why can't I pay with xbox credit on Xbox?

I got a 15 Euro Xbox credit card, but I would like to buy an Xbox 360 game, but it says, "You have no valid payment method to add" what do I want to have the game, I have an xbox one s.

Xbox 360 games can only be paid for with a credit card

But I don't have a credit card, 😭

Well, that's the way it is

Then use PayPal.

Not true, PayPal works as well.

You need a credit card to use backward compatibility.

As already written, this is not true.

If a PayPal account is deposited with Microsoft, you can buy 360 or original Xbox games.

In addition, neither had anything to do with backward compatibility. Because it always exists.