I have a multisite with two very different webshops (let's call them SITE1 and SITE2), however now I have a few customers with user accounts on SITE1 who also want to sign up and buy items on SITE2 (and vice versa), but they get this error when they try to sign up to the site they haven't already signed up for:

'Sorry, that email address is already used!’

I guess this error occurs because it is a multisite and hence the email already exists in the user table. but obviously it should be possible for customers to sign up as users to both sites individually as they have no idea the two sites are part of a multisite.

I tried to add the snippet from here:


... and it worked in regards to signup. A customer can now sign up to both sites individually and I see the email connected to a user on site 1 and site 2.

BUT: Lost password request for this new user does not work on site2 (I signed up first on site1). It says: "Invalid username or e-mail."

Apparently it does not accept the email address, but it does accept username (a username customer never sees as they use their email as login. In this case the username is tatjana_h_3, but only I as an admin can find this in the users profile)

But password has not been changed and password is actually not the issue here, because it appear I can log in with her username (a username the customer never gets as she uses her email to log in) and the same password as always.

2 Answers 2


You could use a plugin such as
Join My Multisite - https://wordpress.org/plugins/join-my-multisite/

The plugin allows you to set if a user is a member of site1 and visits site2, automatically add site2 to the user's sites. So you avoid them making another account.

  • Plugin no longer available.
    – BooBailey
    Commented May 6, 2019 at 17:07

I've just released a plugin network-subsite-user-registration for WordPress 4.7+ for users registration on subsites of a Network / Multisite.

This overcomes the issue with "auto joining plugins" like Ipstenu's great "Join My Multisite" plugin (that I've enjoyed using for years) .. the problem being that the user has to have an account already before you can give access to another site.

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