if( ! function_exists( 'videotube_prevent_access_backend' )  ){

    /*
     * Redirect members to custom url while accessing backend.
     */

    function videotube_prevent_access_backend() {

        // The custom url goes here.
        $custom_url = '';

        if( is_user_logged_in() && ! current_user_can( 'administrator' ) && is_admin() && ! empty( $custom_url ) ){
            wp_redirect( $custom_url );
            exit;
        }
    }

    add_action( 'admin_init' , 'videotube_prevent_access_backend' );
}