Login Redirect from Comments

um-login-redirect.php

<?php
/**
* Ultimate member - Redirect Comment to UM Login page on “You must be logged in to post a comment”.
* URL: https://wordpress.org/support/topic/email-domain-restriction-at-registration/
*/
// Change Default Comment Login link to UM Login Page.
add_filter( 'comment_form_defaults', 'um_change_login_link' );

if ( ! function_exists( 'um_change_login_link' ) ) {
    function um_change_login_link( $defaults ) {
        if ( class_exists( 'UM' ) ) {
            $defaults['must_log_in'] = '<p class="must-log-in">' . sprintf( __( 'You must be <a href="%s">logged in</a> to post a comment.' ), um_get_core_page( 'login' ) ) . '</p>';
            return $defaults;
        }
    }
}