Messenger error 10: Message sent outside the 24-hour window

Code 10 with subcode 2534022 is the plain statement of the standard messaging window rule. Meta's error-codes table pairs the message "This message is sent outside of allowed window" with the one-line explanation: "Apps can only send a message to a customer within 24 hours of receiving the customer's message." The person last engaged more than 24 hours ago, and the send carried no tag or opt-in token that would authorize it anyway.

This subcode appears throughout the current Messenger Platform documentation generation (it sits in the 253xxxx block shared with the Instagram messaging API, where the same window applies), while 2018278 is its older Messenger-specific sibling with the "learn more about the new policy" wording. Which one you receive varies by surface and API version; handle them identically. On the Instagram side the same rule and subcode family are covered in the Instagram messaging guide.

Everything else about the request was acceptable: token, permissions, recipient. The remedy set is the standard one, get the person to re-engage (any inbound message, postback or comment reopens the window for 24 hours), use the HUMAN_AGENT tag within 7 days for human escalations if your app is approved for it, or use an opt-in mechanism collected earlier. Since April 27, 2026 the retired update tags are not an option; they fail with code 100.

{
  "error": {
    "message": "(#10) This message is sent outside of allowed window.",
    "type": "OAuthException",
    "code": 10,
    "error_subcode": 2534022,
    "fbtrace_id": "Fz54k3GZrio"
  }
}

One window gate for all outbound traffic: compute eligibility at send time from the latest qualifying event, and select untagged, tagged or opted-in delivery automatically. Collect opt-ins at conversation peaks, right after a purchase or booking, when consent is natural. The window-opening actions and every escape hatch are tabulated in the Messenger limits reference; the policy history is in the troubleshooting guide.