Socket connection failed when I am using knowledge Id and startVoiceChat

I'm using the @heygen/streaming-avatar SDK to create an interactive avatar. My implementation includes generating a token, initializing the avatar, and setting up event listeners. However, I'm encountering a WebSocket connection error:

WebSocket connection to 'wss://api.heygen.com/v1/ws/streaming.chat?session_id=...&session_token=...' failed:

I am using a custom avatar with a knowledge base Id that I have created. I also initialized the voice chat using startVoiceChat. The avatar is not speaking and It is not event listening to my audio. Could this issue be related to the free API plan, or is there something I'm missing in my setup?