---
title: "Send chat message"
method: POST
path: "/v3/chats/{chat_id}/messages"
tags: ["v3", "chats"]
---

# Send chat message

`POST /v3/chats/{chat_id}/messages`

## Request

- Base URL: `https://api.mentium.io` (the document declares no server; this is the origin it was published from)
- URL: `https://api.mentium.io/v3/chats/{chat_id}/messages`
- Auth: HTTP bearer

Store the message and start the chat's agent on it; its steps and reply are listed as they are written. 409 while the agent is still answering the previous message.

## Path parameters

- `chat_id` string, uuid, required

## Headers

- `mentium-workspace-id` string, nullable

## Request body

- AgentChatMessageCreate
  - `text` string, required

## Response `201`

Successful Response

- AgentChatMessageOut: One row of a chat: a user message, an agent step, an approval request or a decision.
  - `id` string, required
  - `chat_id` string, required
  - `kind` 'user' | 'assistant' | 'tool_call' | 'tool_result' | 'approval_request' | 'approval' | 'error' | 'summary', required
  - `role` string, nullable
  - `text` string, required
  - `payload` object, nullable: Kind-specific fields (see libs.chat.contracts)
  - `turn_id` string, nullable: Id of the user message that started this row's turn
  - `seq` integer, required: Cursor for listing; rows are ordered by it
  - `created_at` string, date-time, required
  - `user_id` string, nullable

## Other responses

- `422`: Validation Error

---

[API](https://skmtc.dev/mentium/apis/mentium-api.md) - [All operations](https://skmtc.dev/mentium/apis/mentium-api/llms.txt) - [OpenAPI document](https://skmtc.dev/mentium/apis/mentium-api/revisions/b4ed8e59432e?raw)