From the WP Admin Area, navigate to Appearance -> Menus
Click on the Custom Links drop down.
Input your popup link in the URL field: ‘#popmake-123‘ where ‘123’ is the ID number of your popup. The popup ID can be found in the WP Admin on the ‘All Popups’ screen, CSS Classes (column).
Set your preferred link text, and click Add to Menu. Save the menu and refresh your site.
From the WordPress Admin Area, navigate to Appearance > Menus
Click on Screen Options in the upper right corner of the screen.
Check the box for CSS Classes. Close the Screen Options pane.
Click on your menu item. You will now see a field to add your own CSS classes at the bottom.
Add the correct `popmake-{integer}` class to your menu item as shown above.
From the WP Admin, open Popup Maker > All Popups > CSS Classes. Find the Popup Maker generated class in the CSS Classes column and enter it into the CSS Classes field on the Menu page.
Save the menu and refresh the site. On the front of the site, click the targeted menu item to display the popup.