Ionic GeoLocation native on iOS returns undefined (not working)


I have started implementing ionic GeoLocation native according to the instructions provided on the ionic site.

Please see below for my code:

    this.platform.ready().then(() => {
        console.log('GEO SERVICE initializeGeoService()');
        let watchPosition = this.geoLocation.watchPosition();
        watchPosition.subscribe((locationData) => {
            console.log('WATCH Lat -> ' + locationData.coords.latitude);
            console.log('WATCH Lan -> ' + locationData.coords.longitude);
            console.log('TIMESTAMP -> ' + locationData.timestamp);
            this.writeGeoDataForUser(locationData.coords.latitude, locationData.coords.longitude,

This seems to be working when I run the app in the Chrome browser. However, when I make an iOS build and run it on an iOS device, I keep getting the following error:

[956:260097] Error: TypeError: undefined is not an object (evaluating ‘locationData.coords.latitude’)**
[956:260097] ERROR: ERROR TypeError: undefined is not an object (evaluating ‘locationData.coords.latitude’)**

Does anyone have experience on how to get this working on iOS? Or has encountered the similar error and was able to resolve it? Thanks in advance.