Click on Add New App/Website
Then Type Your App Name and Select Android
Click on Edit Depending on your App For Android edit Android And Same for the IOS
Now Create New Project in Firebase
Click On Setting icon And select Project Setting
Click Android and IOS What Ever you want
Now type your Package id and register
After completing Now click on Setting icon and click Project setting and cloud Message here you will find firebase server key and firebase sender id
Now add firebase server key on OneSignal and firebase Sender id and click next
Select Ionic Cordova and click next
Now You Will Find your OneSignal id
Paste OneSignal id to api.service.ts