[Home](./index.md) > [@digitalpersona/authentication](./authentication.md) > [SmsOtpAuth](./authentication.smsotpauth.md) > [sendChallenge](./authentication.smsotpauth.sendchallenge.md) ## SmsOtpAuth.sendChallenge() method Sends an SMS challenge with a OTP code to the user's registered mobile device. Signature: ```typescript sendChallenge(user: User): Promise; ``` ## Parameters | Parameter | Type | Description | | --- | --- | --- | | user | User | a name of the user | Returns: `Promise` a promise to send the challenge code.