Xbox 1 month needed

Important At the end of the first (free) month, membership automatically renews to a paid membership that renews monthly by default. The membership will renew to the payment method that was added to your account. If you don’t want the membership to
renew, you must turn off automatic renewal. You can read more on the Free Xbox LIVE Gold Trial - Xbox Support

Page here.

You can always contact support and speak with a billing agent, they will be able to access your account and
They can Add Or Remove information for you. They can also update your Payment Methods. You can reach out to them by visiting this page here You
can always check out the International Xbox Support phone numbers for your region by clicking here

Amazon has a digital store too so that if you buy from there you get the code emailed to you, rather than a physical item sent to you with a code on it. Other retailers also do this, although it might depend on region whether it's offered to you.

It could say your address is wrong if your account is set up in the wrong region, so that it is expecting, for example, a US address and you're giving it a UK one. You should verify that this is not the case.

You need to buy at least 1 month of Xbox live instead of the free month

You're absolutely right:

"Prepaid codes can be used to extend an Xbox Live subscriptions or for games, entertainment, and other special offers."

Note the word PREPAID though. Prepaid suggests that the code has already been fully paid for. A prepaid subscription code (Gold, Season Pass, etc), a prepaid game (some are out there) or other prepaid offers.

A currency code is not a prepaid code. Currency is an amount of money that you purchase a code for so you can apply it to your account so you can easily purchase games/dlc for the account. There is currently no way to purchase a Gold membership with the
currency on your account.

There are also other things on the marketplace that you cannot use currency for such as the EA Access program on the Xbox One. This is due to the fact that those memberships are recurring memberships and the company needs a guarantee that there will be
money on the account when the membership renewal comes due.