Delivery app - suppliers wants continuous bell even if app is closed till action

Brief Explanation - Order taking app. When new order comes, suppliers get notified using a PUSH notification and SMS . But they want - A Bell should keep ringing till they Accept or Reject the order and this should happen even if the app is closed.

I am using Ionic 4 , Cordova and Firestore .

I tried to join custom sound notification, a long sound but found that beyond android 8, it is also not possible and there is no success found on web too.

What else can I do to achieve this requirement. Other apps which do this, how do they work ?