Amazon Native Ads – Why are mine not displaying?

I have copied and pasted the code for Amazon Native Ads below some individual posts in my Editing pages but there is nothing displaying from Amazon – there’s just a small blank space beneath my posts where the ads box should appear. I’ve even tried placing the code in my “Header and Footer” plugin under Post Content but still the ad box does not display. Why is this? Could it be my theme? I’m using Colinear theme by Automattic.