Architect API: Triggering shared common module flows from inbound flows

Trying to refactor our inbound flows to hit a shared verification module via the Architect API. The docs show /v2/architect/flows/shared for defining the module, but I can’t find the endpoint to actually invoke it from a standard inbound flow.

The trigger action in the inbound flow JSON only accepts specific flow IDs, and passing the shared flow ID returns a 400 Bad Request. How do I wire this up without duplicating the logic across every inbound flow?