sender_throttled

HTTP 429. Abuse signals tripped, so the sender may not start conversations for a while.

What it means

Flow protects senders from being banned by the channels. When a sender sends the same text to many new contacts, gets many starts with no reply, or gets blocked, it is throttled and you receive sender.status_changed. Replies into existing conversations still go.

Why it happens

The same first message to many new contacts.
Many conversations started that nobody answered.
Contacts blocking the sender.

How to fix it

Wait retry_after seconds; the sender recovers by itself. Personalise first messages and start only conversations people expect.

{"error": {"type": "sender_throttled", "retry_after": 3600, "sender": "snd_...",
  "hint": "Wait 3600 seconds before starting conversations from snd_...; meanwhile reply only into existing conversations."}}

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.