I have integrated, according to the Instant Articles documentation, Audience Network ads, but I'm getting "HTTP error 503" as a server response.
This is the code that is implemented:
https://www.facebook.com/adnw_request?placement=PLACEMENT_ID&adtype=banner300x250
But my ad is not showing. Does anyone know why this is happening? Thank you.
Bjorn is correct, the app id you're using is most likely a regular AN app id. You would need to create an IA specific AN app id through the page you're trying to publish articles from through IA. Here's a blog post that explains the procedure: https://developers.facebook.com/ia/blog/post/2016/04/08/self-service-audience-network/