Thank you so much for reaching out, I hope that this finds you well today.
Taking a look into your question, I wanted to confirm for you up front that Customer.io's integration with Twilio is one-way, meaning that you can only use our integration to send outgoing SMS messages. We handle this by making use of Twilio's Messaging API. This API is used for sending transactional and marketing SMS messages, and can also be used to send mass messages via our SMS Broadcast feature.
That said, Twilo's documentation does show that you can send custom responses to replies from your customers. Again, I do want to note that those replies go to Twilio's servers and do not come back to Customer.io, so our integration would not be able to handle replies natively, but it appears you can do this within Twilio according to their documentation.
The first link below is using Twilio Studio Flows, which is Twilio's built-in no-code/low-code app builder, which is set up very similarly to Customer.io's workflow builder (Twilio Studio documentation here). The second link below is to their API documentation which is language specific, should you prefer to have your engineering team set up an application to handle replies and even auto-responses to the SMS messages you trigger from Customer.io.
So, in conclusion, it would appear that you can achieve what you're needing through Twilio's tools/API. The reason that the handling of replies and auto-responses must be handled within Twilio is that the Customer.io integration can only send messages, and is not designed to receive replies back from your campaigns.
I hope that this helps to provide clarity for you here, Sean! If you have any further questions or need anything additional from our side, please do let us know. Cheers and have a great week ahead!
I figured out a solution and posted about it here: