> ## Documentation Index
> Fetch the complete documentation index at: https://flow.engineer/docs/llms.txt
> Use this file to discover all available pages before exploring further.

# not_implemented

> This endpoint or channel is not live yet during the beta.

HTTP 501. This endpoint or channel is not live yet during the beta.

## What it means

Flow Messaging is in beta. Some endpoints and channels are in the spec before they are live, and answer `not_implemented` until then.

## Why it happens

* Asking for an iMessage line, a WhatsApp number or a US SMS number with `POST /v0/senders`: these are connected by the Flow team, not by API. This answer comes first, with a test or a live key.
* An endpoint that arrives in a later release.

## How to fix it

Build on what is live now (Telegram, iMessage replies, and the endpoints that answer). For an iMessage line, a WhatsApp number or a US SMS number, write to the Flow team at [samyak@flow.engineer](mailto:samyak@flow.engineer) or [prabal@flow.engineer](mailto:prabal@flow.engineer) with your app ID (`GET /v0/app`) and the number's details, never secrets or tokens; it then appears in `GET /v0/senders` with your live key. Meanwhile, build and test on simulated conversations of that channel with a test key (`POST /v0/test/conversations` with `"channel": "imessage"`, `"sms"` or `"whatsapp"`): they keep the channel's rules and need no number.

```bash
curl https://api.flow.engineer/v0/senders -H "Authorization: Bearer $FLOW_MESSAGING_KEY"   # what you can send from today
```

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.