Instagram error 10: Message sent outside of allowed window

This is Instagram's messaging-window refusal, and the single most-searched Instagram messaging error. Meta's error reference states it plainly: "Apps can only send a message to a customer within 24 hours of receiving the customer's message." The clock starts at the person's last inbound message and every automated send after it expires is rejected with code 10 and subcode 2534022. At send time the message string is usually the longer variant: (#10) Message failed to send because more than 24 hours have passed since the customer last replied to this account.

Nothing is broken. Your token is valid, your permissions are granted, the recipient exists, and the same payload would deliver fine inside the window. The type: OAuthException and code 10 make this look like the permission failure described under bare (#10), which is why the subcode matters: 2534022 is the window, no subcode is permissions. Retrying does nothing - the window only reopens when the person messages you again.

Instagram is stricter here than its sibling platforms. There are no re-engagement templates like WhatsApp's, and the Messenger message tags (ACCOUNT_UPDATE, CONFIRMED_EVENT_UPDATE, CUSTOMER_FEEDBACK) are documented as "Not available for Instagram Messaging API." The one sanctioned exception is the human_agent tag: a message from a human agent may be sent within 7 days of the user's message, and only after your app is approved for the Human Agent feature through App Review. Tagging automated messages with it is a documented policy violation.

{
  "error": {
    "message": "(#10) Message failed to send because more than 24 hours have passed since the customer last replied to this account.",
    "type": "OAuthException",
    "code": 10,
    "error_subcode": 2534022,
    "fbtrace_id": "AbCdEfGh1234"
  }
}

Treat the window as a scheduling constraint, not an error to handle. Persist last_inbound_at per Instagram-scoped ID, check it before every send, and collect whatever you need from the person while the conversation is live. The full window rules, including the 7-day human-agent extension and the private-reply window, are tabulated in the Instagram limits reference, and the troubleshooting guide walks through telling this apart from the permission form of code 10.