add this code to theme function.
// Instant Articles Recirculation Ads Filter
add_filter( ‘instant_articles_transformed_element’,’m_add_recirculation_ad’ );
function m_add_recirculation_ad ($instant_article) {
$instant_article->addMetaProperty(‘fb:op-recirculation-ads’, ‘placement_id=YOUR-PLACEMENT-ID’);
return $instant_article;
}
replace YOUR-PLACEMENT-ID with your audience network placement id