Adsterra API supports only popunder auto-import. If you want to import banners you may easily make it manually.
You need to know two things: banner code and zone_id.
Go to Adsterra panel, find your website and placement code, and ID, see screenshot below. Before coping code and placement_ID make sure your website is Approved and placement is Active.

Copy and paste Adsterra Placemant_id to Zone_id in AdSpyglass, Adsterra code to AdSpyglass code box:
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After you insert Code and Zone_ID click save button: