[Forminator] - Make user registration form respect the registration settings of the multisite network

wpmudev-forminator-prevents-new-sites.php

<?php
/**
* Plugin Name: [Forminator] - Make user registration form respect the registration settings of the multisite network
* Plugin URI: https://wpmudev.com/
* Description: Forces the option set on the following path: Network Dashboard > Settings > Network Settings > Registration Settings
* Author: Glauber Silva @ WPMUDEV
* Author URI: https://wpmudev.com/
* Jira Task: SLS-308
* License: GPLv2 or later
*/

defined( 'ABSPATH' ) || exit;

/**
 * Before creating a new site, check if the option chosen in
 * "Network Dashboard > Settings > Network Settings > Registration Settings" allows this...
 * Otherwise, it blocks the creation of the new site by Forminator.
 */
function wpmudev_intercept_multisite_validation( $validate, $custom_form, $submitted_data, $is_approve ) {
	if ( is_multisite() ) {
		/**
		 * Registration Options:
		 * 'none' => 'Registration is disabled'
		 * 'user' => 'User accounts may be registered'
		 * 'blog' => 'Logged in users may register new sites'
		 * 'all'  => 'Both sites and user accounts can be registered'
		 */
		$registration = get_site_option( 'registration' );
		if ( 'blog' !== $registration && 'all' !== $registration ) {
			$custom_form->settings['site-registration'] = false; // Prevents new site registrations by Forminator.
		}
	}
	return $validate;
}
add_filter( 'forminator_cform_user_registration_validation', 'wpmudev_intercept_multisite_validation', 0, 4 );