Add mobile notifications to webapp (Android & iOS)

We have a webapp based on Firebase which updates a variable called java_value every time the value is updated on the database. We have a local user variable called numuser. When numuser = java_value, a notification must alert the user, regardless if mobile screen is off. This is achievable in Android using Service Workers, but we are unsure how to implement on iOS. Please indicate how you will develop notifications for Android and iOS in your proposal. We will only accept bids below $40.000 CLP, so please bid accordingly. thank you