When somebody opts-in or opts-out of SMS for my business, how can I send that info back to my service?

Hi, we currently have our environment set up so that when a user replies "stop" they are opted-out of Ringcentral automatically. Can I somehow send this back to my service so that we can store this data on our end?

I was thinking If I sent a text I can have my service look for a error code, but I don't see an error code specifically for opt-in scenarios.

What's the best way to accomplish this?