I am using ringcentral api for ringout in Dev sandbox. But unfortunately I am getting exception:
"message": "Forbidden", "errorCode": "InternationalProhibited"
If you are using Dev sandbox as you said in your question, that is free service for developers on Sandbox, and international calling is prohibited there.
check the link:
Using the RingCentral Phone for Desktop, you can dial or receive test calls, send and receive test SMS or Fax messages in your sandbox environment.
Download RingCentral Phone for Desktop:
Tip: switch to the "sandbox mode" before logging in the app:
1 Person is following this question.