In order to include menu on a Max Mega Menu menu you need to add a php output code like this:

First in functions file make sure that register_nav_menus is defined. Here is an example of theme setup function:

if ( ! function_exists( 'ua0_setup' ) ) :
	function ua0_setup() {
		load_theme_textdomain( 'ua0', get_template_directory() . '/languages' );
		add_theme_support( 'automatic-feed-links' );
		add_theme_support( 'title-tag' );
		add_theme_support( 'post-thumbnails' );
		register_nav_menus( array(
			'menu-1' => esc_html__( 'Primary', 'ua0' ),
		) );
		add_theme_support( 'html5', array(
		) );
		add_theme_support( 'customize-selective-refresh-widgets' );
add_action( 'after_setup_theme', 'ua0_setup' );


After you can add menu to the desired location. Make sure that menu name matches the name setup in previous step.

<?php wp_nav_menu( array( 'theme_location' => 'menu-1' ) ); ?>