All your numbers are SMS enabled. What made you think it's not enabled, how did you send messages and what was the error message?

I use the API, the response is successful. But I can't receive the SMS.

The example message Id: 12871924004

The same problem using the https://app.devtest.ringcentral.com/

There was an issue with SMS in all sandbox numbers in the last few days. The issue was resolved yesterday evening. Please retest and let us know if it still does not work for your numbers.