Create Meta Instagram Post Ad

Turns an EXISTING Instagram post/Reel into an ad (Ads Manager's "Use existing post → Instagram"). No new creative — the organic Instagram media runs as-is. This WORKS TODAY and needs no Instagram content permission: it is a pure Marketing API write (AdCreative source_instagram_media_id + instagram_user_id, no object_story_id). ig_media_id is the Instagram media id — from list_meta_instagram_posts (media_id, including its advertised_media list) or from Ads Manager → Use existing post → Instagram. The connected Instagram account is resolved automatically from page_id, or from the ad account when neither page_id nor ig_user_id is given; pass ig_user_id directly (list_meta_instagram_accounts) when the account has no Facebook Page. CLICK-TO-WHATSAPP / MESSENGER FROM AN ORGANIC POST: welcome_message = the ready-written text that auto-populates the person's WhatsApp/Messenger compose box (without it the thread opens empty, so it looks like the business started the conversation and the business's auto-reply never fires), greeting = optional in-thread greeting, ice_breakers = up to 4 tappable quick replies (≤80 chars each; they replace the auto-fill). Engagement still accrues on the ORGANIC post. Leave cta_type empty and the button is derived from the ad set's destination_type — that is the normal path; only pass cta_type (WHATSAPP_MESSAGE / SEND_MESSAGE) together with link when you want to override it, because Meta rejects a call-to-action with no link on this creative. Advantage+ creative enhancements are OFF by default; pass enhancements only to explicitly enroll named features, and the result verifies the enrollment. To add a welcome message to an ad that ALREADY exists, use update_meta_instagram_post_ad — it keeps the organic post, the ad id and its learning. The ad is created PAUSED and goes through Meta review. confirm=false = preview.