Before testing the service, following things to be checked:
correct client I'd and secret, username should be phone number and extention number should be correct and allowed permission and correct url based on environment like sandbox/ production
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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