500 code issues are mostly from server side if the service is down for a particular moment. This can be due to various reasons like high traffic, network issue or maintenance mode.
The service may come up after some time automatically resolving the issue
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:
2 People are following this question.