Verizon has told me that they are likely blocking RingCentral sending from the centralized numbers because: This scenario is common and usually occurs because Verizon is flagging the automated messages from RingCentral as spam due to new stricter carrier registration requirements (10 DLC). While manual messages might pass, a high volume of automated or templated messages can get blocked if RingCentral is not properly registered.
automated messages often contain links, repetitive phrasing, or similar templates that trigger spam filtering systems. There are known issues with the RingCentral notifications failing to deliver specifically the numbers via the SMS gateway.
If RingCentral changed it so that the SMS message came from our phone number that has SMS enabled it likely would not be blocked.

This is a problem for us that occurred several months ago and must be corrected by Verizon or I may change carriers

this feature used to be available through Verizon - but they suddenly stopped. We used this feature to alert our on call technicians to "after hours" call in customer emergencies.
We are an emergency service company monitoring critical research and life sciences equipment.

Why would you or verizon NOT allow this? Makes no sense.