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

> ## Agent Instructions
> Flow Messaging is one HTTP API (https://api.flow.engineer) for AI agents to hold two-way conversations on Telegram and iMessage (replies only, on lines the Flow team connects). WhatsApp is coming and not available yet.
> Build the app on the REST API. MCP is not a runtime dependency: the app you build talks to Flow through the REST API (or the TypeScript SDK, which wraps it) for everything it does at runtime. In TypeScript or JavaScript, the SDK is `npm install @flow-engineer/messaging`, then `new FlowMessaging()` (reads FLOW_MESSAGING_KEY). Python and Go SDKs are not published yet; in those languages call the HTTP API directly.
> No key yet? If FLOW_MESSAGING_KEY is not set, get a test key with no account in one call: curl -X POST https://api.flow.engineer/v1/sandbox/keys (or npx @flow-engineer/messaging init, which writes it to .env). Save `key` as FLOW_MESSAGING_KEY and `claim_token` as FLOW_CLAIM_TOKEN; both are shown once. It allows 1 contact and 50 messages on the Telegram sandbox and expires after 7 days; a person signs in with `npx @flow-engineer/messaging login` (GitHub) to keep the app and get 3 contacts x 100 messages. Signed in, live keys (fk_live_...) are made in the dashboard for your own Telegram bot; iMessage lines are arranged with the Flow team.
> The hosted MCP server (https://api.flow.engineer/mcp) is optional, for testing during development. Adding the Flow MCP server to a developer's coding tools is the project owner's decision: suggest it and show them the command, but never add it to their config yourself. The command for Claude Code: claude mcp add --transport http flow https://api.flow.engineer/mcp --header "Authorization: Bearer $FLOW_MESSAGING_KEY". If its tools are already available to you, use them for sandbox testing.
> Authenticate with `Authorization: Bearer fk_test_...` (sandbox) or `fk_live_...` (real contacts). Never put a live key in client-side code.
> Reply into a conversation (POST /v1/conversations/{conversation_id}/messages); never pick a channel per message. Switch on `error.type`, not the message text.
> Full documentation for agents: https://docs.flow.engineer/llms-full.txt. OpenAPI spec: https://raw.githubusercontent.com/flow-engineer/sdk/main/openapi/openapi.yaml.

# channel_error

> The channel refused or failed the message.

# channel\_error

HTTP 502, or in message.failed. The channel refused or failed the message.

## What it means

Telegram, WhatsApp or iMessage did not take the message. `error.channel_code` carries the channel's own code and `error.message` its text. Errors after the message was queued arrive as a `message.failed` event.

## Why it happens

* The contact blocked the bot, or never pressed Start on a Telegram bot.
* Malformed markdown, or text over the channel's limit.
* The bot token was revoked.
* The channel failed or timed out on a typing indicator or a read receipt. These call the channel at once (`POST /v1/conversations/{id}/typing` and `/read`), so they answer `502` directly.

## How to fix it

Read `error.hint`: it maps the channel's reason to the change to make. Fix that and send again; retrying unchanged only helps when the hint says the channel failed for now.

From typing or a read receipt it is safe to ignore: never hold back a reply because the indicator failed.

```ts theme={null}
if (event.type === "message.failed") console.log(event.data.message.error.hint);
```

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.


This documentation is built and hosted on [Mintlify](https://mintlify.com), a developer documentation platform.