SMS Not Enabled In Sandbox

Please read this post and open a dev support ticket.

@Phong Vu thanks for the info, can I promote my app to production without testing sms feature in sandbox? I already have the code required to send sms and have tested it on my other ring central account, and it's working fine. Can we just promote my app to production? I am not inclined to buy mobile number for sandbox account just for testing purpose.

Yes I can manually move your app to the production for this case. Give me the app client id.