Hi @DesperateCoder , you’re not doing it “wrong,” HubSpot’s naming just makes it easy to get turned around the first time. If your goal is a messaging system API-only that still shows up in Inbox/Help Desk, the “Custom Channels” route is the right mental model.
A thread is the message chain, and messages live inside that thread. Custom Channels is basically how you’re allowed to create and feed those threads from an external system, while still using the same underlying Conversations threads/messages endpoints to read and append to them (so yes, it all converges back into the Conversations platform). The official custom channels guide is the cleanest place to anchor the flow and required objects (https://developers.hubspot.com/docs/api-reference/conversations-custom-channels-v3/guide )
Two important gotchas. First, Custom Channels is not supported with legacy private apps, so if you were hoping to do this with a private app only, you’ll hit a wall and need a public app setup instead (that note is in the Custom Channels docs). Second, “new chain vs follow-up” is something you control: you create a new thread when you decide it’s a new conversation, and you POST a message to the existing threadId when it’s a follow-up. That “send message to an existing thread” behavior is documented here (Accounts Dashboard | HubSpot )
One quick question that affects the whole design: do you need agents to work these conversations inside HubSpot’s Inbox/Help Desk UI, or is this purely a backend messaging store with no human-in-HubSpot requirement? Attachments especially can push you toward one approach vs another depending on where you want the files to live.