Popunder code not in the <body>. Please make sure that you placed popunder code as the first item of <body> on every page where you want to trigger popunder.
Make sure that you have removed old popunder codes from your website. Codes from ad networks will conflict with AdSpyglass code.
Data-spots and/or data-tag parameters are missing, Re-take popunder code from AdSpyglass panel. It should contain Data-spots and data-tag tags.