Hi, I'm Elise, a fellow user like yourself and I'd be happy to help with your issue.
Unfortunately recovery keys should be all numbers, that is why you can't type letters.
It seems like you may have the recovery key ID, rather than the key itself.
You can find help on locating your key here:
https://support.microsoft.com/en-us/windows/fin...
Please let me know if you need any further assistance.
Kind Regards,
Elise