Hello, I'm Quinn and here to help!
This error usually happens when the region of the gift purchase is different from the region set on the account redeeming the code. Please check that both accounts have the same Country/Region:
- Go to https://account.microsoft.com/profile
- Verify the Country/Region on both your account and your girlfriend’s account.
If the regions already match and the code still cannot be redeemed, I recommend to contact Microsoft Support so they can review the purchase and assist with a replacement code or refund:
- Go to https://support.microsoft.com/home/contact
- In the search box, type Contact Support
- Click Get Help
- Scroll down and click Contact Support
- In *Products and services, *select Windows
- In Category, select Technical Support
- Click Confirm, and choose Choose a support option available