## Add members

`POST /v1/chats/:chatId/users`

Adds one or more users to a group chat.

## Parameters

| Parameter | Type | Required | Description |
|----------|-----|:-----:|---------|
| `chatId` (path) | number | yes | Numeric chat ID (without the `chat` prefix) |
| `format` (query) | string | no | `v2` turns on the v2 mode — see "The v2 mode" below. Any other value is ignored and the response is unchanged. A repeated `format` is not rejected: with `format=v1&format=v2` the last value wins, so the v2 mode is on, while `format=v2&format=v1` returns the legacy response. The bracket form `format[]=v2` turns on the v2 mode when all its values are `v2` |

## Request fields (body)

| Field | Type | Required | Description |
|------|-----|:-----:|---------|
| `users` | number[] | yes | Non-empty array of user IDs to add. Each element is a positive integer: a number, or a string of decimal digits without leading zeros or spaces, up to 2^53−1; any other shape is refused before Bitrix24 is called |
| `hideHistory` | boolean | no | `true` — new members do not see the history from before they joined, default `true`. `false` — the history is open from the moment the chat was created |

**The v2 mode.** `format=v2` adds the members through the v2 messenger with the same body. Only `users` — at most 50 IDs per request — and `hideHistory` are accepted: the Bitrix24 spellings `USERS` and `HIDE_HISTORY`, other body fields and query parameters are rejected with `400 INVALID_PARAMS`, and `hideHistory` must be a boolean. The `hideHistory` default is the same — `true`. `data` carries `{ "result": true }` instead of `true`.

## Examples

### curl — personal key

```bash
curl -X POST "https://vibecode.bitrix24.com/v1/chats/123/users" \
  -H "X-Api-Key: YOUR_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{ "users": [42, 53] }'
```

### curl — OAuth application

```bash
curl -X POST "https://vibecode.bitrix24.com/v1/chats/123/users" \
  -H "X-Api-Key: YOUR_APP_KEY" \
  -H "Authorization: Bearer USER_SESSION_TOKEN" \
  -H "Content-Type: application/json" \
  -d '{ "users": [42, 53] }'
```

### JavaScript — personal key

```javascript
const res = await fetch('https://vibecode.bitrix24.com/v1/chats/123/users', {
  method: 'POST',
  headers: {
    'X-Api-Key': 'YOUR_API_KEY',
    'Content-Type': 'application/json',
  },
  body: JSON.stringify({ users: [42, 53] }),
})

const { success, data } = await res.json()
console.log('Added:', data)
```

### JavaScript — OAuth application

```javascript
const res = await fetch('https://vibecode.bitrix24.com/v1/chats/123/users', {
  method: 'POST',
  headers: {
    'X-Api-Key': 'YOUR_APP_KEY',
    'Authorization': 'Bearer USER_SESSION_TOKEN',
    'Content-Type': 'application/json',
  },
  body: JSON.stringify({ users: [42, 53] }),
})

const { success, data } = await res.json()
```

### curl — the v2 mode

```bash
curl -X POST "https://vibecode.bitrix24.com/v1/chats/123/users?format=v2" \
  -H "X-Api-Key: YOUR_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{ "users": [42, 53], "hideHistory": false }'
```

## Response fields

| Field | Type | Description |
|------|-----|---------|
| `success` | boolean | Always `true` on success |
| `data` | boolean | `true` when added successfully |
| `data.result` | boolean | The v2 mode: `true` — the request was carried out |

## Response example

```json
{
  "success": true,
  "data": true
}
```

## Error response example

403 — the API key does not have the `im` scope:

```json
{
  "success": false,
  "error": {
    "code": "SCOPE_DENIED",
    "message": "This endpoint requires 'im' scope"
  }
}
```

## Errors

| HTTP | Code | Description |
|------|-----|---------|
| 400 | `INVALID_CHAT_ID` | `chatId` is not a positive integer — checked before the Bitrix24 call |
| 400 | `MISSING_PARAMS` | The `users` field is absent or the array is empty (including a request without a body at all) |
| 400 | `INVALID_PARAMS` | `users` is not an array, or one of its elements is not a positive integer in canonical form (the index and type are named in `message`; `"047"`, `" 47"` and values above 2^53−1 are refused). In the v2 mode also `users` longer than 50, a query parameter other than `format`, a body field other than `users` and `hideHistory`, a `hideHistory` that is not a boolean, a body that is not a JSON object. Nothing was sent to Bitrix24 |
| 403 | `WRITE_BLOCKED_READONLY_KEY` | The key is read-only — see [access rights](/docs/access-rights) |
| 403 | `SCOPE_DENIED` | The API key does not have the `im` scope |
| 401 | `TOKEN_MISSING` | The API key has no configured Bitrix24 tokens |
| 422 | `BITRIX_ERROR` | Bitrix24 returned an error — the text is in the `message` field (for example, chat not found or no permission). The Bitrix24 code is in `error.b24Code`. Without `format`, adding members to a collab chat returns this error with `ACCESS_ERROR` and the text `It is forbidden to add users to this chat`. In the v2 mode the member is added |
| 502 | `BITRIX_UNAVAILABLE` | Bitrix24 is unavailable or returned a server error |

Full list of common API errors — [Errors](/docs/errors).

## Known specifics

**Numeric IDs only.** Bitrix24 casts each element of `users` to a number by PHP rules: a word becomes `0` and is silently skipped with an "added" response, and a nested array crashes Bitrix24. To keep a typo from looking like a success, the API checks the elements itself: it accepts a number or a string of decimal digits without leading zeros or spaces, and returns `400 INVALID_PARAMS` for anything else.

**Nonexistent users are skipped.** If the `users` array contains IDs of nonexistent or inactive users, they are ignored without an error. The remaining users are added.

**CoPilot joins a workgroup chat along with a new member.** When you add a member in the v2 mode to the chat of a group created with [`POST /v1/workgroups`](/docs/entities/workgroups/create), the CoPilot system bot with `bot: true` also appears among the members. If you remove the bot, it comes back when the next member is added to the chat. This does not happen in a group chat created with [`POST /v1/chats`](/docs/chats/management/create).

**History is hidden by default.** When adding without an explicit `hideHistory`, new members do not see messages sent before they joined. To give new members access to the history from when the chat was created, pass `hideHistory: false`.

## See also

- [Chat members](/docs/chats/members)
- [List members](/docs/chats/members/list)
- [Remove a member](/docs/chats/members/remove)
- [Chat management](/docs/chats/management)
- [Chats](/docs/chats)