Restrict register certain domains

I can’t think of any reason why it wouldn’t work as all the normal hooks will be available. looking into the user.php hook description it states “If any errors are present in $errors, this will abort the user’s registration.” could this be your issue ?

e.g. things like where your username or email address is used and already and registered to a different subsite.

add_action('register_post', 'is_valid_email_domain', 10, 3);
function is_valid_email_domain($login, $email, $errors)
{
    $allowed_domains = ['test.com', 'auto.com'];
    $valid = false;
    foreach ($allowed_domains as $domain) {
        $d_length = strlen($domain);
        $current_email_domain = strtolower(substr($email, -($d_length), $d_length));
        if ($current_email_domain === strtolower($domain)) {
            $valid = true;
            break;
        }
    }
    // Return error message for invalid domains
    if ($valid === false) {
        $errors->add('domain_whitelist_error', pll__('<strong>Error</strong>'));
    }
}

This is in functions.php. If plugin is in use all domains seems to be allowed for some reason. I tested this function with vanilla (single site) WP installation and it works.

Try it with a multi site install without the NSUR plugin active. Does that work?
It may also be impacting you that foe multisite registration is actually on the main site (for network registration) so it may need to be added there to.

hi @topi_r … how did you get on ?
I’m going to close this ticket now. however, if you want more support just continue here.