Hi, I just want to share some information one of the developers shared with me a while back. Sorry but I totally forgot about this. Read below….
You can instruct your users to use their “Email Address” in the username field. And then in the future they will be able to use that to log into the site.
Our plugin has TWO columns in the database for username and email (they can be the same) but they BOTH require a value. You can’t get rid of one of the fields. We need these fields because the Core WordPress system uses the username and email address fields for WP users. We integrate with WP so we maintain the same architecture which makes the integration very easy.
Bottom line, both of those fields require a value when using our plugin. (Quoted by Admin)