the /call/id endpoint does not seem to provide a transcript while the call is on-going. I see the listenUrl, but that seems like its only for realtime audio. I know webhook does send transcript data. but is there another way to just get the latest transcript data for an on-going call via rest api?

via rest api - No, transcript can only be pushed via webhooks in real time as of now.

Vapi doesn’t support fetching live transcripts via REST, use the Server URL webhook for real-time updates or the listenUrl WebSocket to stream audio and handle transcription yourself..