# Send an SMS

Source: https://joinsimplesms.com/docs/api/messages/send
Index: https://joinsimplesms.com/llms.txt

`POST /v1/messages`

Sends an SMS from one of your numbers. In test mode the message is simulated: it reaches `delivered` but no text is sent (`simulated: true`, an X-SimpleSMS-Simulated header, and a `notice` when `to` is a real-looking number). The one exception is a send to your own verified phone, which is really delivered when a verification sender is available (`simulated: false`). `from` may be omitted when the account has exactly one number for the key's mode (the sandbox number with a test key, the one live sending number with a live key); with none or several the request is refused and the error lists the choices under `numbers`. Supports the Idempotency-Key header, including with scheduled_at. A live send from a US local number that is not yet linked to an approved registration (sender.state other than active) is delivered only to your verified numbers; to anyone else it answers 403 sender_not_registered with an X-SimpleSMS-Sender-State header (test_only | pending | action_needed).

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.

## Headers

| Name | Type | Required | Description |
| --- | --- | --- | --- |
| `Idempotency-Key` | string | No | Makes retries safe for 24 hours: the same key and body replays the original successful response (with Idempotent-Replayed: true); a different body returns 409. Failed requests release the key. At most 255 characters. |

## Request body

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

| Field | Type | Required | Description |
| --- | --- | --- | --- |
| `to` | string | Yes | Example: `+15005550006`. |
| `from` | string | No | One of your numbers, or a sender pool id (pool_...): SimpleSMS picks a pool member, the same one for each recipient every time. Optional when the account has exactly one number for the key's mode. Example: `+15005550100`. |
| `body` | string | Yes | At most 1600 characters. |
| `customer_id` | string | No | Optional. Attribute to one of your customers. Defaults to the customer the from-number is assigned to; a number assigned to another customer is rejected (400). |
| `scheduled_at` | string | No | Optional. Future ISO timestamp (or epoch ms), up to 30 days out. The message is queued and the response is a scheduled_message object instead of a message. |
| `media` | array of string (uri) | No | Reserved for MMS; currently returns 400 mms_not_enabled. |

## Responses

| Status | Meaning | Body |
| --- | --- | --- |
| 201 | Message accepted | `Message` |
| 202 | Accepted and queued: a temporary carrier failure is being retried automatically (status queued, next_attempt_at set) | `Message` |
| 400 | Invalid request | `Error` |
| 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` |
| 409 | Idempotency conflict | `Error` |
| 429 | Rate limit or quota exceeded | `Error` |
| 502 | The carrier permanently rejected the message (carrier_error) | `Error` |

### 201: `Message` fields

| Field | Type | Description |
| --- | --- | --- |
| `id` | string | Example: `msg_a1B2c3D4e5F6g7H8`. |
| `object` | `message` |  |
| `to` | string | Example: `+15005550006`. |
| `from` | string | Example: `+15005550100`. |
| `body` | string |  |
| `direction` | `outbound`, `inbound` |  |
| `status` | `queued`, `sent`, `delivered`, `failed`, `received` |  |
| `test` | boolean |  |
| `simulated` | boolean | True when nothing was handed to a carrier: every test-key message except one sent to your own verified phone. Always false on live messages. A simulated message still reaches `delivered`. |
| `notice` | string | Only on the response to POST /messages. Present when a test-key send to a real-looking number was simulated: says nothing was sent and how to send for real. |
| `schedule_id` | string | The recurring schedule this message is an occurrence of. Present only when set. |
| `created_at` | string (date-time) |  |
| `media` | array of string (uri) | MMS attachments (inbound today). |
| `sent_by` | string | Console user or API key that composed it. |
| `failure_reason` | string | The carrier's raw text for a failed send. Kept for compatibility; see `failure`. |
| `attempts` | integer | Live sends: carrier submissions so far. More than 1 means it was retried. |
| `next_attempt_at` | string (date-time) | Present while queued for an automatic carrier retry. |
| `receipt_status` | `missing` | The carrier accepted the message but sent no delivery report within 72 hours. status stays sent. |
| `customer_id` | string | The customer this is attributed to. Present only when set. |
| `timeline` | array of object | Every status transition, oldest first. Inbound messages have a single `received`. |
| `timeline[].status` | `accepted`, `validated`, `queued`, `sent_to_carrier`, `carrier_accepted`, `retry_scheduled`, `delivered`, `failed`, `received` |  |
| `timeline[].at` | string (date-time) |  |
| `timeline[].attempt` | integer | Carrier attempt this step belongs to (from sent_to_carrier on). |
| `segments` | integer | Parts the body is split into (GSM-7: 160, then 153 each; UCS-2: 70, then 67). Example: `1`. |
| `encoding` | `gsm7`, `ucs2` |  |
| `price` | object | What this message costs, in USD. One all-in rate per outbound message; carrier fees are included (a 0 line). Null on messages sent before prices were recorded. Nullable. |
| `price.total` | number | Example: `0.009`. |
| `price.currency` | `usd` |  |
| `price.breakdown` | array of object |  |
| `price.breakdown[].label` | string |  |
| `price.breakdown[].amount` | number |  |
| `destination_carrier` | string | The recipient's mobile carrier, when a cached lookup knows it. Nullable. |
| `failure` | Failure | Null unless status is `failed`. Nullable. |

## Errors

| Status | When |
| --- | --- |
| 400 | Invalid request |
| 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 |
| 409 | Idempotency conflict |
| 429 | Rate limit or quota exceeded |
| 502 | The carrier permanently rejected the message (carrier_error) |

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"
  }
}
```

## Idempotency

Send an `Idempotency-Key` header to make retries safe. For 24 hours the same key with the same body replays the original successful response (with `Idempotent-Replayed: true`); the same key with a different body returns 409. A failed request releases its key.

## Examples

### curl

```bash
curl -X POST "https://api.joinsimplesms.com/v1/messages" \
  -H "Authorization: Bearer $SIMPLESMS_API_KEY" \
  -H "Content-Type: application/json" \
  -H "Idempotency-Key: 6f1c2f0e-order-1042" \
  -d '{
  "to": "+15005550006",
  "from": "+15005550100",
  "body": "Hello from SimpleSMS"
}'
```

### Node.js

```javascript
import { SimpleSMS } from 'joinsimplesms'; // npm install joinsimplesms

const sms = new SimpleSMS(process.env.SIMPLESMS_API_KEY);

const message = await sms.messages.send({
  from: '+15005550100',
  to: '+15005550006',
  body: 'Hello from SimpleSMS',
});

console.log(message.id, message.status);
```

### Python

```python
import os
from joinsimplesms import SimpleSMS  # pip install joinsimplesms

client = SimpleSMS(os.environ["SIMPLESMS_API_KEY"])

message = client.messages.send(
    to="+15005550006",
    body="Hello from SimpleSMS",
    from_="+15005550100",
)

print(message["id"], message["status"])
```

## Related

- Guide: [Messages](/docs/messages)
- [All messages endpoints](/docs/api#messages)
- [API reference](/docs/api)