Handling 'joinGroup' and 'sendToGroup' events in Azure PubSub with Azure Functions

Question

I have an Azure PubSub service with an event handler configured using Azure Functions.

With a basic web socket connection from a React app I can connect, send messages, and trigger events in Azure Functions.

Client side JS:

const ws = new WebSocket("http://myservice.azure.com");
    ws.onopen = () => {
      ws.send("message");
    };

Azure Functions:

[FunctionName("NotificationConnected")]
        public static void Connected(
        ILogger logger,
        [WebPubSubTrigger("notification", WebPubSubEventType.System, "connected")] ConnectedEventRequest request,
        BinaryData data,
        WebPubSubDataType dataType)
        {
            logger.LogInformation("Request from: {user}, data: {data}, dataType: {dataType}",
                request.ConnectionContext.UserId, data?.ToString(), dataType);

        }

[FunctionName("NotificationMessage")]
        public static async void NotificationMessage(
        ILogger logger,
        [WebPubSubTrigger("notification", WebPubSubEventType.User, "message")] UserEventRequest request,
        BinaryData data,
        WebPubSubDataType dataType)
        {
            logger.LogInformation("Request from: {user}, data: {data}, dataType: {dataType}",
                request.ConnectionContext.UserId, data.ToString(), dataType);

        }

The above all works as expected and both functions fire. I want to enable group level messaging using the json.webpubsub.azure.v1 sub protocol so on the client side I now have:

const handleMessage = (message: any) => {
        const container = JSON.parse(message);
        if (container.ackId === 1) {
          ws.send(JSON.stringify({
            "type": "sendToGroup",
            "group": state.group,
            "ackId": ++ackId,
            "dataType": "text",
            "data": "group message"
          }));
        }
      }

    const ws = new WebSocket("http://myservice.azure.com", "json.webpubsub.azure.v1");
    ws.onopen = () => {
      ws.send(JSON.stringify({
        type: 'joinGroup',
        group: state.group,
        ackId: ++ackId
      }));
    };

ws.onmessage = function (e) {
  handleMessage(e.data);
};

In Azure PubSub I can see the client connecting to the group and sending messages to the group, and the 'connected' function still fires in Azure Functions but the 'message' function doesn't.

How can I bind to the joinGroup and sendToGroup events now in Azure Functions?