# Issue a one-time password that can be used to step-up a token

Initiates the step-up token process by sending an SMS with an one-time-password to a device belonging to the logged-in user that was previously enrolled through `/authentication_factors/otp/{channel}` endpoint.
This process is required for endpoints that require a step-up token to complete the call.
*Note that on the Sandbox Environment, text messages are not sent and the one-time-password is always "123456".*

Endpoint: POST /stepup/challenges/otp/{channel}
Version: v3
Security: auth_token, api-key

## Path parameters:

  - `channel` (string, required)
    The unique identifier for the channel.

## Header parameters:

  - `idempotency-ref` (string)
    A unique call reference generated by the caller that, taking into consideration the payload as well as the operation itself, helps avoid duplicate operations. Idempotency reference uniqueness is maintained for at least 24 hours.

## Response 400 fields (application/json):

  - `message` (string)
    When present helps to identify and fix the problem.

  - `syntaxErrors` (object)
    Is returned as part of an HTTP error response whenever a syntax error is detected. A list of the fields together with their syntax error will be provided.

  - `syntaxErrors.invalidFields` (array)

  - `syntaxErrors.invalidFields.params` (array)

  - `syntaxErrors.invalidFields.fieldName` (string)

  - `syntaxErrors.invalidFields.error` (string)
    Enum: "REQUIRED", "HAS_TEXT", "REQUIRES", "SIZE", "RANGE", "IN", "NOT_IN", "REGEX", "EXACTLY", "AT_LEAST", "AT_MOST", "ALL_OR_NONE"

## Response 403 fields (application/json):

  - `errorCode` (string)
    Enum: "INSUFFICIENT_PERMISSIONS"

## Response 405 fields (application/json):

  - `code` (string)

  - `message` (string)

## Response 409 fields (application/json):

  - `errorCode` (string)
    Enum: "CHANNEL_NOT_SUPPORTED", "CHANNEL_NOT_REGISTERED", "MOBILE_NUMBER_INVALID", "MOBILE_COUNTRY_NOT_SUPPORTED", "RETRY_IN_15SEC", "CHALLENGE_LIMIT_EXCEEDED"

## Response default fields (application/json):

  - `code` (string)

  - `message` (string)