When i sent sms with my production, It's error : "The requested feature is not available"
but it working with sandbox :
My production app key :
Have you checked the below references:
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:
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