Hey Shane!
Nice to meet you! I'm Darhyl, an Independent Advisor.
25-character codes can only be redeemed once on a Microsoft account and not to a device. This means that you need to locate the Microsoft account where you have redeemed your Microsoft Flight Simulator 2020 codes.
Sign in to all of your Microsoft accounts on account.microsoft.com > Order History > Select the date range when you redeemed your Microsoft Flight Simulator 2020
Once you have found the account where the game was redeemed, sign in to that account on the Microsoft Store app > Library > Games > and then your redeemed game should appear on that tab ready to install.
You may also check this link for reference: https://flightsimulator.zendesk.com/hc/en-us/articles/360019392440-How-to-redeem-your-Microsoft-Flight-Simulator-code-on-your-Microsoft-account
Thank you for your kindness and understanding! Please feel free to let me know if you need anything else.
Best Regards,
Darhyl