When you send a message using the streaming endpoint(POST HTTP Request), Salesforce Agent API sends back the responses using the server-sent event (SSE) protocol.
Salesforce Agent API can be invoked synchronously too. Check the following Blog Post for Synchronous Salesforce Agent API processing.
Pleas use the above Salesforce Agent API Blog Post to setup Connected App and other crucial steps in order to send the Stream Messages HTTP Post request.
Header:
Body:
Using the server-sent event (SSE) approach, we can improve the user experience by listening to the events and update the UI experience for the users.