To be able to use TextUs with your RingCentral numbers, you'll need to request that RingCentral opt those numbers out of SMS.
Please submit a SMS Opt Out Request to RingCentral's Salesforce/Tier1 Support. You will be instructed what to do from there. If you have questions about how to submit a ticket, please contact your RingCentral Account Representative.
Once the opt out process has been completed, RingCentral will send you an "LOA" (Letter of Authorization). You will then need to send this over to our team so we can SMS enable the numbers through our Provider and create your Accounts.
Please reach out to firstname.lastname@example.org with any questions!