I am still trying to understand how tools work underline. to be more specific I don't know how Vapi consume the response from the api call. Hope someone can help: I created a custom tool which will ping me server. during the test I confirm that my server received the call and response were sent:

res.status(200).json({
            results: [
                {
                    toolCallId: req.body.message.call.id,
                    result: 'The receiver is currently not available',
                },
            ],
        });

On the tool definition side, I guess I just need to use the tool description

check if the current receiver is available for a call. The response will be a sentence like "the receiver is available now to take the call" or "the receiver is NOT available now.

But it does not work. So can someone help me understand how Vapi process the response from tool calls?