Duo MFA send email attribute

Hi!
I’m attempting to setup MFA with Duo. I have setup the WebSDK app in Duo and created a new rule in Auth0 for Duo and copied the ikey, skey and host as per the documentation. When users go to my application to sign in they enter their credentials (Auth0) and are then prompted to Enroll in Duo. Once enrolled they can access the App, HOWEVER, this creates a new user in Duo with a cryptic random username and counts as an additional enrollment and license. What I want to do is to use the user’s existing enrollment. What do I need to modify for Auth0 to send the email address attribute to Duo so user is recognized as an existing user in Duo?
Thank You