Using arbitrary Strings as Event names are allowed. For e.g.
Facebook.logEvent('InvoicePage', {}, 1).then(function (value) {console.log('fulfilled logevent'); }, function (reason) {console.log('failed logevent'); });;
where Facebook is referred from :
import {Facebook} from "ionic-native";
One reason for the analytics not showing up is if you had to change the APP_ID or APP_NAME for some reason. To fix this, remove and install "cordova-plugin-facebook4" using
ionic plugin remove cordova-plugin-facebook4 --save
and reinstall using with the new values
ionic plugin add cordova-plugin-facebook4 --variable APP_ID="new_app_id" --variable APP_NAME="myApplication"