deivideandrade OneSignal notification works even if chrome is running in the background (even if on lockscreen)
But for continuous ringing stuff cannot be achieved with a web app and there are many other limitations for webapp and even pwa.
We are aware that store owner app is very important to be powerful so that actions can be taken quickly and easily without losing any business. Hence for the cloud Foodomaa version we have started works on the Native android Store Owner application. Full set features will be provided soon.