---
title: "Send Message or Request Revision"
method: POST
path: "/v3/video-agents/{session_id}"
tags: ["Video Agent"]
---

# Send Message or Request Revision

`POST /v3/video-agents/{session_id}`

Sends a follow-up message to an existing session. Use to answer agent questions, add context, or request edits to a generated video. Only valid for sessions created in chat mode.

## Path parameters

- `session_id` string, required

## Request body

- SendMessageRequest — Request body for sending a follow-up message, answering the agent's question, or requesting edits and revisions to a previously generated video.
  - `message` string, required — Text message to the agent
  - `avatar_id` string, nullable — Override avatar for this message
  - `voice_id` string, nullable — Override voice for this message
  - `brand_kit_id` string, nullable — Brand kit ID to apply for this message
  - `files` union[], nullable — Optional file attachments (max 20 files)
    - union
      - AssetUrl — Asset input via publicly accessible HTTPS URL.
        - `type` 'url', required — Input type discriminator
        - `url` string, required — Publicly accessible HTTPS URL for the asset
      - AssetId — Asset input via HeyGen asset ID from the asset upload endpoint.
        - `type` 'asset_id', required — Input type discriminator
        - `asset_id` string, required — HeyGen asset ID from the asset upload endpoint
      - AssetBase64 — Asset input via base64-encoded content.
        - `type` 'base64', required — Input type discriminator
        - `media_type` string, required — MIME type of the encoded content (e.g. "image/png")
        - `data` string, required — Base64-encoded file content

## Response `200`

Successful response

- object
  - `data` SendMessageResponse — Response from sending a message to a session.
    - `session_id` string, required — Session ID
    - `run_id` string, required — Run ID for this message processing
    - `title` string, nullable — LLM-generated session title

## Other responses

- `400` — Invalid request parameters
- `401` — Authentication failed
- `404` — Resource not found
- `429` — Rate limit exceeded

---

[API](https://skmtc.net/heygen/apis/heygen-external-api.md) · [All operations](https://skmtc.net/heygen/apis/heygen-external-api/llms.txt) · [OpenAPI document](https://skmtc-service-staging.skmtc.workers.dev/v1/apis/heygen/heygen-external-api/revisions/e2e54726e210/schema)