Send a message

POST/chat-rooms/:roomId/messages

Post a message to a chat room. Send `content` as JSON for a text message, or a `file` as multipart/form-data for an image message. Only room members can post.

Auth	Login required

Path parameters

roomIdstringrequired

Chat room ID.

Request body

contentstring

Message body; required for text messages.

filefile

Image file (when sending as multipart/form-data)

replyToIdstring

The message being replied to. Must be a non-deleted message in the same room.

mentionsobject[]

Mentions, as `[{ userId, name }]`. The `name` must appear in `content` as `@name` (entries that do not are ignored). Only users returned by GET /chat-rooms/:id/mention-candidates are accepted. Up to 20 per message (400 beyond that). Send it as a JSON string when using multipart.

Request
curl https://api.4s.link/chat-rooms/ROOM_ID/messages \
  -X POST \
  -H "Authorization: Bearer 4s_at_..." \
  -H "Content-Type: application/json" \
  -d '{
  "content": "@山田太郎 よろしくお願いします",
  "mentions": [{ "userId": "a1b2c3d4-...", "name": "山田太郎" }]
}'

Example response
{
  "id": "m1a2b3c4-...",
  "type": "USER",
  "content": "よろしくお願いします",
  "imageUrl": null,
  "createdAt": "2026-08-18T00:00:00.000Z",
  "user": { "id": "a1b2c3d4-...", "slug": "taro", "firstName": "太郎", "lastName": "山田", "avatarUrl": "https://.../avatar.png" }
}