Meta Instagram Accounts

Lists the Instagram accounts usable from a Meta ad account. It finds Instagram accounts when list_meta_pages shows no Page, or when the Instagram account is not linked to a Page. FOUR sources are merged, so an account the Ads Manager 'connected Instagram accounts' list omits is still found: (1) act_{id}/connected_instagram_accounts, (2) the legacy instagram_accounts edge, (3) the ad account's own AD HISTORY (adcreatives → instagram_user_id) — an Instagram account this ad account has already advertised from is usable even when both link edges are empty, (4) the FACEBOOK PAGE BRIDGE — in practice an Instagram business account is linked to a Page, not to the ad account, so the Pages assigned to this ad account (and, when nothing else was found, the user's other Pages) are read for instagram_business_account.

Each entry: ig_user_id (pass it to list_meta_instagram_posts or create_meta_instagram_post_ad), username, and `source` (ad_account_link | previously_advertised | page_linked). For page_linked entries check `usable_from_this_ad_account`: false means the Instagram account exists and is linked to a Page, but that Page is not assigned to this ad account — the blocker is the Page assignment, not Instagram. An EMPTY list means no Instagram account is reachable from this ad account; it is added in Meta Business Suite → Settings → Accounts → Instagram accounts, then 'Assign to people and assets' → this ad account. A missing account here usually indicates a sharing/permission gap rather than a non-existent account; check every returned `source` first, and check list_meta_pages(account_id=...) for the Page-assignment cause. account_id comes from list_meta_ad_accounts. Every matching account is retained: limit controls only this response page (0 = as many as fit), and page_token=next_page_token retrieves the cached remainder without another Meta request or credit.