Django channel group_send all messages to one channel in the group

Question

I am trying to make a real time chat web app with Django channel. When I am trying using Postman build multiple WS connections with it. I encountered some weird thing, let's say I have 2 connections to the same server at 8000 port. Then I send a message via group_send, ideally each connection will get 1 message, but it turn out 2 messages are send to the newer connection.

Here is my consumer:

class RealtimeConsumer(AsyncJsonWebsocketConsumer):
    async def websocket_connect(self, event):
        user_id = self.scope['user']
        await self.channel_layer.group_add(
            str(user_id),  # use id as the group name
            self.channel_name
        )
        await self.accept()
        await self.send_json(
            {
                "connectionKey": self.channel_name,
                "clientId": str(user_id),
            },
        )

    async def send_message(self, event):
        message = event["message"]
        await self.send_json(
            {
                "messages": message,
                "connectionKey": self.channel_name,
            },
        )

    async def websocket_disconnect(self, message):
        user_id = self.scope['user']
        await self.channel_layer.group_discard(
            str(user_id),  # group name
            self.channel_name
        )

Send to group func:

def send_single_user_msg(channel_name, message):
    channel_layer = get_channel_layer()
    async_to_sync(channel_layer.send)(
        channel_name, {
            'type': 'send_message',
            "text": message,
        }
    )

I'm using local redis server as the channel layer.