Unable to reset MacBook - invalid Find My account - AKAuthenticationError code 7003

I am attempting to reset my Macbook Air M1 just to clean up a little. I get past the apple ID password stage, then it asks me for a password to turn off Find My.

The first password prompt asks me for the password for my current Apple ID.

The second time, though (for Find My), it asks me to unlock my old Apple ID email address (I've switched to an @icloud.com address a while back). After I enter the same password (since it is in fact the same account that it is asking for), I get the "Your account has been locked error". When I Proceed and try to unlock it, i get the AKAuthenticatonError Code 7003.

I am therefore unable to reset my Mac, even though I have full access to my Apple ID and all of the necessary credentials.

What can I do, this is a time-sensitive matter that I would like to resolve as quickly as possible.

Thank you for any input.