I don't know where did you get 12 digits secret key, but Microsoft MFA worked for me with 16 characters secret key. Maybe you provided the wrong value. I've got 16 characters MFA Microsoft secret key this way:
1) Go to MFA setup window by this Microsoft Documentation:
1.1) Sign in to myapps.microsoft.com.
1.2) Select your account name in the top right, then select profile.
1.3) Select Additional security verification.
2) Click "Set up Authenticator app".
3) Click "Configure app without notifications".
You should see 16 characters secret key value (it contains spaces, but you need to remove them).
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I don't know where did you get 12 digits secret key, but Microsoft MFA worked for me with 16 characters secret key. Maybe you provided the wrong value. I've got 16 characters MFA Microsoft secret key this way:
1) Go to MFA setup window by this Microsoft Documentation:
1.1) Sign in to myapps.microsoft.com.
1.2) Select your account name in the top right, then select profile.
1.3) Select Additional security verification.
2) Click "Set up Authenticator app".
3) Click "Configure app without notifications".
You should see 16 characters secret key value (it contains spaces, but you need to remove them).