1: Once The Pantograph Extensions plugin is activated Mega Menu is available in your admin panel dashboard.
2: Enable WPBakery for Mega Menu
a. Navigate to WPBakery > Role Manager
b. In Post Types choose ‘Custom’ and then make sure mega_menu is checked.
3: Now add mega menu item in Main Menu from the Appearence>Menus and click on Screen Options to expand the options. And check the Mega Menu and CSS Classes item. And select Main Menu from Select a menu to edit: and press Select button.
4: Now you see the Mega Menu on the left side; you can select this mega menu item and click on the Add to Menu button. Drag the mega menu item and use it as a child menu for a parent menu. In the parent menu need to expand and add css class ‘dropdown megamenu’
Finally, Save Menu from right side.