Every flow sends and receives messages as a specific Flow user — the identity (flow/user account) that shows up in chat when the flow talks to someone. Each flow has its own client identity rather than messages appearing to come from a generic system account.
When you configure a flow you are asked which Flow user should be sending and handling messages. Each “Flow user” is a new API client. You must be an admin to create a new “flow user” or API client.
Related docs: A Quickstart Guide, Keywords