When utilizing the Instagram Graph API Content Publishing endpoints to publish media (Posts or Reels) containing the collaborators array parameter, the media is successfully generated and published to the feed. Furthermore, checking the container via the backend confirms that the invitation status correctly registers as "Pending".

However, the target username is not sent any notification on web or mobile.

No system push notification fires, and no entry appears in the user's native Activity Feed (heart icon). The invite remains completely invisible to the target user unless they manually navigate the source IG's posts tab to look for the passive confirmation banner. This issue universally affects accounts across the board.