Hi, apologies for the inconvenience. Have you reported this to support? Sign out and sign in and monitor it for 24-48hrs. If the issue still exists, please create a case here: https://support.ringcentral.com/contact-support.html. I appreciate your patience in this matter.
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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