Skip to main content

​
outside_window

HTTP 409, or error.type in a message.failed event. The channel will not deliver outside its conversation window.

​
What it means

On WhatsApp you may send free-form messages only within 24 hours of the contact’s last message. After that, WhatsApp accepts only approved templates; the send is refused with HTTP 409. On iMessage a line can reach only contacts who have messaged it (or opted in). The send is accepted, and the refusal arrives later as a message.failed event with outside_window. Typing and read receipts go to the channel at once, so they answer HTTP 409 outside_window directly when the channel’s window is closed: on iMessage, typing works only within 5 minutes of the contact’s last message.

​
Why it happens

  • WhatsApp: the contact last wrote more than 24 hours ago.
  • WhatsApp: you are starting a conversation with someone who never wrote to the number.
  • iMessage: the contact has never messaged the line, or has not opted in to it.
  • iMessage: you turned typing on more than 5 minutes after the contact’s last message.

​
How to fix it

On WhatsApp, send an approved template (content.type=template), or wait for the contact to write again; their message reopens the window. GET /v1/capabilities?conversation=... shows window.open and window.open_until.
On iMessage, ask the contact to message the line first (share its handle, or its opt-in link from the sender’s address.link when the line has one, for example in your app or website), then reply in the conversation their message opens. From typing or a read receipt, ignore it and send your reply: the indicator is a courtesy, and the reply itself is not affected. Every error also carries hint, one sentence specific to your request, and doc_url, this page. Coding agents connected to Flow’s MCP server (https://api.flow.engineer/mcp) can call explain_error with the type to read this page.