Yiicod/yii2-socketio notification for one user in multi-server environment

yiicod/yii2-socketio

I am currently using notifications (oneSignal) to send requests for a specific user to get approval (accept/reject). The issue is that mobile app users might turn off notification and we are not able to send the request for them. (this is done through the api in yii2advanced project).

what I thought of is that I need to create a table for the requests in database and each user will get his requests through an API but this is not realtime user still have to refresh.

so I decided to go for websocket and I found this extension. but I don’t think the documentation was enough for me to understand everything and start the implementation.

I have a lot of questions. where can I put the code of websocket in my api project? how will mobile app developers connect to it? how can I scale websockets in multiserver environment? is redis the only solution? can we use mysql?