# Subscribe or unsubscribe a contact from a topic

Source: https://joinsimplesms.com/docs/api/contacts/set-topic
Index: https://joinsimplesms.com/llms.txt

`PUT /v1/contacts/{id}/topics/{topic}`

`topic` is a topic id or name. Recorded in the consent ledger and the audit log. No record means subscribed, so only an unsubscribe narrows who is sent to. Subscribing to a topic does not lift an opt-out.

Send your API key as a bearer token: `Authorization: Bearer ssms_sk_...`. Test keys run this endpoint against the [sandbox](/docs/sandbox); see [Authentication](/docs/authentication) for key modes and scopes.

## Path parameters

| Name | Type | Required | Description |
| --- | --- | --- | --- |
| `id` | string | Yes | Contact id or phone number |
| `topic` | string | Yes | Topic id (tp_...) or name |

## Request body

JSON (`Content-Type: application/json`).

| Field | Type | Required | Description |
| --- | --- | --- | --- |
| `subscribed` | boolean | Yes |  |
| `source` | string | No | Where the change came from, e.g. "preference_page". Default "api". |

## Responses

| Status | Meaning | Body |
| --- | --- | --- |
| 200 | The new state; `changed` is false when it already was | JSON object |
| 401 | Missing, malformed, or revoked API key | `Error` |
| 402 | Billable live calls only: the prepaid credit balance cannot cover the call (insufficient_credits); nothing was done or charged | `Error` |
| 404 | No such contact, number, or topic | `Error` |
| 429 | Rate limit or quota exceeded | `Error` |

### 200: response fields

| Field | Type | Description |
| --- | --- | --- |
| `object` | `topic_subscription` |  |
| `phone` | string |  |
| `contact_id` | string | Nullable. |
| `topic_id` | string |  |
| `name` | string |  |
| `subscribed` | boolean |  |
| `changed` | boolean |  |

## Errors

| Status | When |
| --- | --- |
| 401 | Missing, malformed, or revoked API key |
| 402 | Billable live calls only: the prepaid credit balance cannot cover the call (insufficient_credits); nothing was done or charged |
| 404 | No such contact, number, or topic |
| 429 | Rate limit or quota exceeded |

Every error has the same JSON shape, and `request_id` matches the `X-Request-Id` response header. [Errors](/docs/errors) lists every code and what to do about it.

```json
{
  "error": {
    "code": "invalid_request",
    "message": "What went wrong, in plain words.",
    "param": "the_field",
    "request_id": "req_a1B2c3D4e5F6g7H8"
  }
}
```

## Examples

### curl

```bash
curl -X PUT "https://api.joinsimplesms.com/v1/contacts/ct_a1B2c3D4e5F6/topics/tp_marketing" \
  -H "Authorization: Bearer $SIMPLESMS_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
  "subscribed": true
}'
```

### Node.js

The Node.js SDK does not wrap this endpoint yet; call it with `fetch`.

```javascript
const res = await fetch('https://api.joinsimplesms.com/v1/contacts/ct_a1B2c3D4e5F6/topics/tp_marketing', {
  method: 'PUT',
  headers: {
    Authorization: `Bearer ${process.env.SIMPLESMS_API_KEY}`,
    'Content-Type': 'application/json',
  },
  body: JSON.stringify({
    "subscribed": true
  }),
});

if (!res.ok) throw new Error((await res.json()).error.message);
const data = await res.json();
```

### Python

The Python SDK does not wrap this endpoint yet; call it over HTTP.

```python
import json, os, urllib.request

req = urllib.request.Request(
    "https://api.joinsimplesms.com/v1/contacts/ct_a1B2c3D4e5F6/topics/tp_marketing",
    method="PUT",
    headers={
        "Authorization": f"Bearer {os.environ['SIMPLESMS_API_KEY']}",
        "Content-Type": "application/json",
    },
    data=json.dumps({
        "subscribed": True
    }).encode(),
)
with urllib.request.urlopen(req) as res:
    data = json.load(res)
```

## Related

- Guide: [Contacts](/docs/contacts)
- [All contacts endpoints](/docs/api#contacts)
- [API reference](/docs/api)