The silenceTimeoutSeconds property is set on the assistant object, not as a standalone call parameter. Here's how to use it:

On the assistant directly:

js
const assistant = await client.assistants.create({
      silenceTimeoutSeconds: 30,
      // ...other config
    });

Per-call via overrides:

js
    const call = await client.calls.createPhone({
      assistantId: "your-assistant-id",
      assistantOverrides: {
        silenceTimeoutSeconds: 30
      },
      customer: { number: "+1234567890" }
    });