Why can’t I redeem a Xbox Game Pass Ultimate code?

You indeed bought a year of Xbox Live Gold subscription, the reason why it was converted to Xbox game pass ultimate is because you have an active Xbox Game Pass Ultimate when you redeem the code.

Sorry but there is no annual Xbox game pass ultimate yet.

If you are already a Game Pass Ultimate subscriber, then any Gold codes you redeem will be converted to Game Pass Ultimate. If you are not an Xbox Game Pass Ultimate Subscriber, then no, the Gold codes should not convert to Game Pass Ultimate.

Hey there EliteCrossFire1,

Thank you for reaching out to us on the forums, if you redeem the Xbox Live Gold code while your Game Pass Ultimate subscription is still active, then you would not be receiving the full time that is shown on the prepaid card.

Xbox Game Pass Ultimate FAQ

"With Xbox Game Pass Ultimate, can I still redeem codes for Xbox Live Gold and Xbox Game Pass?

Yes, These codes will automatically convert to Xbox Game Pass Ultimate at a ratio based on the ERP (Estimated Retail Price) of those codes. Conversion rates are subject to change"

If you want to keep the Ultimate subscription then you can redeem your code but just keep in mind that you won't receive the full time shown on the card as it will convert the time according to the price of the Ultimate. If you want to stop using the Ultimate
subscription then I would advise that you wait for the subscription to expire before you redeem the Xbox Live Gold subscription.

I hope this helps.

The below is taken from the
Gamepass FAQ:

After you join Xbox Game Pass Ultimate, you can continue to redeem Xbox Live Gold and Xbox Game Pass codes. These codes will automatically convert to Xbox Game Pass Ultimate at a ratio based on the ERP (Estimated Retail
Price) of those codes. Conversion ratio subject to change.

The reason why this happens is that your Ultimate includes both Live Gold and GamePass and your voucher is therefore redeemed and converted to reflect this. There is also always a warning before and Live Gold or Gamepass voucher is being added to an ultimate
subscription as mentioned by Salmoro.

If you had Xbox Game Pass Ultimate already active before you redeem that code, when you enter a code for Xbox Live Gold or Xbox Game Pass it will add as Game Pass Ultimate and not only Xbox Game Pass, is this your case?