A 503 usually points to a server-side/service availability issue rather than your microphone pipeline.
Since the audio capture still works, you checked that requests are sent, you have made no code changes and it started suddenly breaking
I would strongly suspect that either there is a Wit.ai backend instability, the API/service changed or you have an expired/invalid app configuration/token.
A few things to check:
- Recreate/regenerate the Wit Server Access Token
- Test with a completely new minimal Wit app/project
- Try upgrading from Voice SDK 69 if possible
Also check if:
- Your app is hitting rate limits
- The endpoint region/service changed
But honestly, repeated 503s with previously working code usually indicate a backend/service issue, not a Unity-side bug.