---
title: "Send an SMS from the inbox number"
method: POST
path: "/api/v1/inboxes/{id}/sms"
tags: ["SMS"]
---

# Send an SMS from the inbox number

`POST /api/v1/inboxes/{id}/sms`

## Request

- Base URL: `https://cooperemail.com`
- URL: `https://cooperemail.com/api/v1/inboxes/{id}/sms`
- Auth: HTTP bearer

Requires message_send. POST returns HTTP 409 outbound_not_registered. HTTP 409 phone_number_not_found when the inbox has no active number. A recipient who replied STOP returns HTTP 409 recipient_opted_out until they reply START. The first message to a recipient adds an opt-out footer. HELP and STOP as the whole body return HTTP 400 reserved_keyword. SHAFT content returns HTTP 400 shaft_blocked. A URL shortener returns HTTP 400 short_link. The body, including the footer, must be 320 characters or fewer (HTTP 400 body_too_long). Outbound segments past the monthly allowance return HTTP 402 plan_limit_exceeded with resource sms_segments. Starter allowance is 100 segments per active number. Pro allowance is 1,500 plus 100 for each active number past the 3 included numbers. Purchased segment packs add 500 each when SMS billing is on. A paused inbox is HTTP 403 inbox_paused. The stored message has channel sms. A later Twilio status callback sets status to delivered, undelivered, or failed, and delivery_events carries the numeric error code. client_id and Idempotency-Key follow the send rules. HTTP 404 not_found when SMS is off.

## Path parameters

- `id` string, required

## Headers

- `Idempotency-Key` string

## Request body

- object
  - `to` string, required: E.164 US or Canada recipient.
  - `text` string
  - `client_id` string

## Response `200`

client_id or Idempotency-Key replay.

## Other responses

- `201`: Sent SMS message.
- `400`: missing_body, reserved_keyword, shaft_blocked, short_link, body_too_long, or invalid_e164
- `402`: plan_limit_exceeded for sms_segments
- `403`: inbox_paused
- `404`: not_found or inbox_not_found
- `409`: outbound_not_registered, phone_number_not_found, or recipient_opted_out

---

[API](https://skmtc.dev/cooperemail/apis/cooper-email-api.md) · [All operations](https://skmtc.dev/cooperemail/apis/cooper-email-api/llms.txt) · [OpenAPI document](https://skmtc.dev/cooperemail/apis/cooper-email-api/revisions/6d800a7b3e33?raw)