---
title: "Start an inbound SMS challenge"
method: POST
path: "/users/@me/phone/inbound-challenge"
tags: ["Users"]
---

# Start an inbound SMS challenge

`POST /users/@me/phone/inbound-challenge`

For very-high-risk registrations the platform requires the user to text a one-time code to the platform's number, instead of receiving a code from the platform. This endpoint generates the code and the destination number to display.

## Response `200`

Success

- InboundSmsChallengeStartResponse
  - `challenge_code` string, required — The numeric code the user must text to our number
  - `our_number` string, required — The Twilio number the user must text the code to (E.164)
  - `expires_at` string, required — ISO timestamp at which the challenge becomes invalid

## Other responses

- `400` — Bad Request - The request was malformed or contained invalid data
- `401` — Unauthorized - Authentication is required or the token is invalid
- `403` — Forbidden - You do not have permission to perform this action
- `429` — Too Many Requests - You are being rate limited
- `500` — Internal Server Error - An unexpected error occurred

## Changes

> 16 revisions in range; 1 not diffed.

- **2026-09-06** `a52a2cf49d9b` — 32 warning
  - added the new `IP_BAN_DECLINED` enum value to the `code` response property for the response status `400`
  - added the new `IP_BAN_DECLINED` enum value to the `code` response property for the response status `401`
  - added the new `IP_BAN_DECLINED` enum value to the `code` response property for the response status `403`
  - added the new `IP_BAN_DECLINED` enum value to the `code` response property for the response status `500`
  - …28 more
  - …this revision’s changelog is incomplete
- **2026-09-05** `4dbb738a3e22` — 4 info
  - removed the `NSFW_EMOJI_STICKER_BLOCKED` enum value from the `code` response property for the response status `400`
  - removed the `NSFW_EMOJI_STICKER_BLOCKED` enum value from the `code` response property for the response status `401`
  - removed the `NSFW_EMOJI_STICKER_BLOCKED` enum value from the `code` response property for the response status `403`
  - removed the `NSFW_EMOJI_STICKER_BLOCKED` enum value from the `code` response property for the response status `500`
- …earlier changes not shown

[Full history](https://skmtc.dev/fluxer/apis/fluxer-api/changes/users/@me/phone/inbound-challenge/post.md)

---

[API](https://skmtc.dev/fluxer/apis/fluxer-api.md) · [All operations](https://skmtc.dev/fluxer/apis/fluxer-api/llms.txt) · [OpenAPI document](https://skmtc.dev/fluxer/apis/fluxer-api/revisions/034cfc3e79b4?raw)