We are using socket io callbacks when sending messages to particular connections. (We use heroku for hosting)

Server emit code looks like

const sockets  = await this.deviceSockets.in(channelName).fetchSockets()
for (const socket of sockets) {
socket.emit(eventName, ...args, function(err, result) {
...
});
}

Client code looks like

socket.on('ping', async (callback) => {
callback({ status: 'ok' })
})

This works fine when we only have one web server running; however when we have multiple webservers running (heroku dynos), we receive the following error when our clients try responding to the callbacks:

Callbacks are not support when broadcasting

However we aren't broadcasting (rather emitting to one particular client)

We are configuring socket-io redis in the following way:

const {createAdapter} = require('@socket.io/redis-adapter')
...
const pubClient = redis.createClient({...})
const subClient = this.pubClient.duplicate()
io.adapter(createAdapter(pubClient,subClient)