Use this shortcode to manually place an ad code within your Instant Articles.
The placement_id parameter is optional, if left blank it will use the default ad placement set on the Ad Settings page of the Plugin. This will only show if you have Ads enabled and a Placement ID can be found. Nothing will appear in the actual post that's shown on your site.
WARNGING Please familiarise yourself with Facebook's advertising policy. Violating them will result in your account being suspended. In particular Ads most be 250 words apart (images count for 70 words) and no ad can be placed at the top of your article.
You can read more about monetising your Instant Articles in the official Facebook Documentation.