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!