Is it possible to integrate custom channels with Studio Flows?
From the documentation, it is possible to trigger a flow using a REST API for the flow.
But it is not clear how to send / get replies from the custom channel after the flow has started.
Twilio developer evangelist here.
Once you trigger a Studio Flow, everything else gets run through the Studio Flow. So you can't, for example, start a Studio Flow with a REST API Trigger by an incoming Twitter DM and then continue the conversation through Studio.