Cannot update user email for Passwordless flow

We are doing passwordless.
Once a user logs in for the first time, we ask for a username and an email address to complete the signup process. We cannot do this on lockjs because passwordless flow does not accept additional signup fields. So we are doing our custom solution, and calling the Management API.

The intention here is to update the email address first, then call for a verification job on Management API.

However the API errors out as “Cannot update email for this user”, I’m guessing this is another limitation of passwordless.

I need users’ emails simply because they need to access their accounts if they change phone numbers. B2C already has this flow, but I don’t see how I can achieve the same functionality on Auth0.