username already exists

this is touched on in the FAQ

Its how WordPress does things for users.

If you think of from WPs view point .. when users are registered on a site from a Network they are known by the whole network. WP has one list of users for a Network, Multi-Network or single WP installation.

NSUR simply opens up the possibilities for limiting/allowing the sub-sites for users to register through. So with NSUR once a user is registered on a sub-site they are known to the whole Network (which is standard WP). The issues comes (as you have seen) that any user trying to register on a second sub-site will get the warning because they are bumping into themselves, or a previous account they created on the Network. If they approached the new sub-site having already logged into the network (through their account made available from their first registration) then NSUR will auto register them with the new sub-site once they enter the admin side.

the weakness is that the user may get confused if they are unaware that the second site is connected to a site they have already registered on. If you have different domain names for the sub-sites then it could lead to confusion. One way to get round this is to have a separate Network on the WP installation for each primary domain, you’ll then be moving into the world of multi-network WP installations which wp-multi-network is a great help for.

(Note there’s been no testing with “WP User Manager” and I’ve not heard of any conflicts)

Thanks for your reply.

Indeed this is very confusing since the user can’t neither register on a second sub-site (“username already exists”) nor reset their password (“username does not exists”) …

I thought while reading the FAQ this conflict is solved by your plugin: My users only register with email (equals username), so according to your FAQ they should be able to register (enable the existing account on a second, third, … subsite) – no ?

I’m not sure how the registering new user can have their entered email and username being the same as user names can only have letters and numbers (so no @ or dot). can you give and example that you are using for your registration form.

also I’ve just tested again by registering an existing network user account with the same username and also their previously used email address and it all works with no messages. They get a prompt that they are now added with a list of the Network sites they belong to.

Can you try one thing temporarily disable your “WP User Manager” plugin and see what happens when you then attempt to re-register an existing user on a new sub-site.
You can then re-enable the “WP User Manager” plugin. Let know if that works ?

I’ve also just added a 2nd demo site to the plugin site so head of to register on both the following as a test to see the experience..
https://justinandco.com/demo/
log out and re-register the same account here
https://justinandco.com/demo2/

Many thanks for your effort!! I might only be able to look into this in January 2020 again. Will keep you posted on my testings.