We run into this issue very often, probably 50% of the Sandbox numbers don't have SMS enabled. Wouldn't it make more sense for RingCentral to ensure that all numbers that are used in Sandbox environments have all features enabled than to have us constantly reaching out to support to enable the feature for one number at a time?
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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