Error when enrolling user in MFA: "MFA is not available for the given first factor. (auth/unsupported-first-factor)"

Question

I'm following the documentation here for enrolling a user in MFA in firebase in a React/Firestore project.

I use passwordless sign in to verify all my users' emails when they create their account. User objects have an email attritbute and emailVerified: true.

I've turned on MFA from the firebase console, pictured below:

When I call phoneAuthProvider.verifyPhoneNumber I get an error:

error Firebase: MFA is not available for the given first factor. (auth/unsupported-first-factor).

I assume this refers to email addresses, but I don't understand why MFA would not be available for this factor.

Answer 1

This was occurring because custom authentication is not a supported provider for MFA. Switching to email link authentication allowed me to use MFA for accounts that had logged in with the email link at least once.

This is not currently reflected in the documentation.