Instagram error 100: Action invalid - app is not the thread owner

Subcode 2534037 comes from conversation routing (the handover protocol): in setups where more than one app handles the same inbox - say an automation app plus a human-agent inbox - exactly one app controls ("owns") each conversation thread at a time, and only the owner may reply. Meta's documented note for this error says you "do not have permission to perform the action on this conversation" and to check permissions, tokens, and - the actual point - thread ownership.

Your app attempted to send or act on a thread while another app (or the Instagram inbox itself, after a human-agent escalation) holds control. The related documented state is the standby webhook channel: apps that do not own a thread receive its events there instead of in messages. If your app replies to standby events as if it owned the thread, this error is the result. It also appears after an escalation flow moves ownership to the inbox and the automation keeps trying to answer.

Model thread ownership explicitly: a per-conversation state machine driven by messaging_handover events, with sends gated on "we own it." Multi-app inboxes without that discipline generate both this error and duplicate replies. The routing requirements, including the app-review expectation that escalated threads transfer to the inbox, are covered by Meta's conversation-routing docs; the connection-level basics live in the troubleshooting guide and the limits reference.