Conversions are being discontinued in AdMob. The Conversions table will continue to display a read-only list of the conversions you’ve created in AdMob and AdWords.
Going forward, all conversions should be created in AdWords and tracked using the Firebase SDK. Once you’ve linked your AdWords and Firebase accounts, you can import conversions from Firebase to see how your ad campaigns drive app installs and in-app actions for your Android or iOS apps.
If you’re setting up conversion tracking in AdWords for the first time, follow the instructions to track conversions with Firebase.