Hello @visaflux
AMP plugin is never intended to serve ads. you may need additional plugins such as google site kit or Advanced Ads.
I am assuming this is your site from replies you created in the previous topic. ( if it’s any different please share your site health information using this form)
Are you using any plugin to insert ads in the header? it might be using wp_body_open or a similar hook to insert the ad on top of the page.
As we can see the site is using reader mode with a legacy theme, have tried to switch to other reader mode themes? ( all the WordPress core theme are AMP compatible, you can find more themes on our site ) so switching reader mode themes might fix your issue easily. our guide has more info on it.
if you want to keep the legacy theme. you can check amp_post_template_body_open hook to insert an ad on top of the page.