## Membership check

`GET /v1/chats/:dialogId/users/membership`

Checks which of the listed users are members of the chat. One request checks up to 50 users at once, for example before inviting users to the chat or mentioning them.

## Parameters

| Parameter | Type | Required | Default | Description |
|----------|-----|:-----:|-----------|---------|
| `dialogId` (path) | string | yes | — | Dialog ID: `chatXXX` for a group chat, a user ID for a direct dialog, or the `me` alias. `chatXXX` is the `id` field of a [recent dialogs](/docs/chats/discovery/recent) row, a user ID comes from the [user list](/docs/entities/users/list) |
| `userIds` (query) | string | yes | — | From 1 to 50 user IDs from the [user list](/docs/entities/users/list) separated by commas, for example `7,12`. Each ID is a positive integer without spaces or leading zeros. A repeated ID is allowed and counts toward the limit of 50 |

Any other parameter or a repeated parameter is rejected with `400 INVALID_PARAMS`.

## Examples

### curl — personal key

```bash
curl "https://vibecode.bitrix24.com/v1/chats/chat123/users/membership?userIds=7,12" \
  -H "X-Api-Key: YOUR_API_KEY"
```

### curl — OAuth application

```bash
curl "https://vibecode.bitrix24.com/v1/chats/chat123/users/membership?userIds=7,12" \
  -H "X-Api-Key: YOUR_APP_KEY" \
  -H "Authorization: Bearer USER_SESSION_TOKEN"
```

### JavaScript — personal key

```javascript
const res = await fetch('https://vibecode.bitrix24.com/v1/chats/chat123/users/membership?userIds=7,12', {
  headers: { 'X-Api-Key': 'YOUR_API_KEY' },
})

const { data } = await res.json()
console.log('Not in the chat:', data.usersNotInChat)
```

### JavaScript — OAuth application

```javascript
const res = await fetch('https://vibecode.bitrix24.com/v1/chats/chat123/users/membership?userIds=7,12', {
  headers: {
    'X-Api-Key': 'YOUR_APP_KEY',
    'Authorization': 'Bearer USER_SESSION_TOKEN',
  },
})

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

## Response fields

| Field | Type | Description |
|------|-----|---------|
| `success` | boolean | Always `true` on success |
| `data.usersInChat` | array | IDs of the requested users who are chat members |
| `data.usersNotInChat` | array | IDs of the requested users who are not chat members |
| `data.users` | array | Brief profiles of all requested users |
| `data.users[].id` | number | User ID |
| `data.users[].name` | string | Full name |
| `data.users[].avatar` | string | Avatar URL. An empty string when no avatar is set |
| `data.users[].color` | string | Avatar color in hexadecimal format |
| `data.users[].type` | string | User type: `user`, `extranet`, `bot` and others |

## Response example

```json
{
  "success": true,
  "data": {
    "usersInChat": [7],
    "usersNotInChat": [12],
    "users": [
      { "id": 7, "name": "John Brown", "avatar": "", "color": "#df532d", "type": "user" },
      { "id": 12, "name": "Anna Smith", "avatar": "", "color": "#1eb4aa", "type": "extranet" }
    ]
  }
}
```

## Error response example

400 — `userIds` was not sent:

```json
{
  "success": false,
  "error": {
    "code": "INVALID_PARAMS",
    "message": "`userIds` is required: 1-50 Bitrix24 user ids separated by commas (4,7), each a positive integer without spaces or leading zeros."
  }
}
```

## Errors

| HTTP | Code | Description |
|------|-----|---------|
| 400 | `INVALID_PARAMS` | `userIds` was not sent, more than 50 IDs were sent, or an ID is not a positive integer. The request has a parameter other than `userIds` or a repeated parameter. Checked before any call to Bitrix24 |
| 403 | `SCOPE_DENIED` | The API key does not have the `im` scope |
| 403 | `WRITE_BLOCKED_READONLY_KEY` | Read-only key, and the chat is not confirmed: a value other than `chatN` was passed and the personal dialog was not found in the same employee's recent dialog list — up to 20 pages and 4000 rows — or the alias creates a dialog. Rejected before any call to Bitrix24 |
| 403 | `WRITE_BLOCKED_READONLY_KEY` | Read-only key that is not an employee's personal key: an application key with a user session, a [management key](/docs/management-keys), or a key with an unconfirmed owner |
| 401 | `TOKEN_MISSING` | The API key has no Bitrix24 tokens configured |
| 404 | `ENTITY_NOT_FOUND` | Bitrix24 answered "not found". The Bitrix24 code is in `error.b24Code` |
| 422 | `BITRIX_ERROR` | Bitrix24 returned an error. The Bitrix24 code is in `error.b24Code`. For a chat that does not exist, the code is `CHAT_NOT_FOUND` |
| 502 | `ME_ALIAS_RESOLUTION_FAILED` | Failed to resolve the user when using the `me` alias |
| 502 | `BITRIX_UNAVAILABLE` | Bitrix24 is unavailable or returned a server error |

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

## Known specifics

**The call may make you a member.** If the chat allows auto-join, the call adds the current user as a member, as when opening a chat. A `READONLY` key may make this call under two conditions: it is an employee's personal key, and the chat is confirmed — `chatN` was passed or the direct dialog was found in the same employee's recent dialogs. The read itself does not mark messages as read. The `im` scope and the user's Bitrix24 access still apply.

## See also

- [Users to mention](/docs/chats/members/mentionable)
- [List members](/docs/chats/members/list)
- [Add members](/docs/chats/members/add)
- [Members](/docs/chats/members)