CB

Currently if you configure username fallback to a non-unique field (pretty much any field other than email) and it matches another user the registration will fail with no means for the user to resolve it. When using fallback it should simply automate making the username unique by checking if it already exists and if it does add random digits to it.

https://www.joomlapolis.com/forum/153-professional-member-support/240011-create-user-with-the-same-firstname-lastname#308290