Dynamically invoke email MFA

Hi all!.

I have the following case. I am employing a custom login form on your app. Users authenticate using their username and password, facilitated by backend communication with the Auth0 Management API.
I am aiming to introduce a feature that allows selected users to opt for email MFA within my app. Once enabled, I need to trigger an email MFA challenge at login via the Auth0 API for the respective user.

I am struggling to find the right documentation page that would help me achieve the desired functionality. Are these capabilities supported by the free plan at all?

Thank you for your time!