We are aware of this error. When we have customers who have this error, we usually have them contact Ring Central developers and create a ticket to provision the sandbox number for SMS.

The customer created a ticket but was given an article instead.
https://medium.com/ringcentral-developers/ringcentral-sms-from-phone-number-fd34fc382181

The system is already working and worked for most customers. There are just customers with a sandbox number not provisioned for SMS that gets the msg-22 error.

Sandbos number: 4702890460

Any help would be appreciated :)
Thanks in advance!