I Have Gold and Game pass on Xbox one X and can't dowload Xbox 360 games.

For 360 content only a credit card or Paypal is considered a valid payment option on the One/website. So if the payment option you have on file is your Microsoft account balance, it will not work.

When you try adding a credit card from the website, try scrolling to the very bottom of the page and changing the region in the bottom left corner to Spain. If it contiues to request US information, then you may need to migrate your account region (for some
reason that gets messed for users on the 360 side of things even if your account already shows as being in the correct region). http://live.xbox.com/accountmigration

Account migation solve the problem, thanks for the help.

Hi, check your details and location at https://account.microsoft.com You will need a valid payment method to purchase 360 games on your Xbox One.

Hi,

Sorry about that issue.

Please read this > support.xbox.com/.../manage-payment-options-on-xbox-one

Now about the 360's purchases you really need a valid payment method even if you are already gold with game pass on the Xbox one...

If still not able to buy it , call Xbox live helpdesk > https://support.xbox.com/contact-us

Regards,

Have you looked at your Microsoft Account to see if it has the correct region? And what happens if you try to add a payment method?

What Smwutches said, look further down the page for Change Region and post back if you don't see it.