SMS Not Enabled In Sandbox

Hello,

I'm trying to test sending an SMS from the sandbox with phone number "12679304303", but I am getting this response:

{

  "errorCode": "FeatureNotAvailable",

  "message": "The requested feature is not available",

  "errors": [

    {

      "errorCode": "MSG-242",

      "message": "The requested feature is not available"

    }

  ]

}

Could someone please enable SMS for my account? Thanks!