Google Store and App Store are two different online stores, supported by Google and Apple respectively.
This is why MarineTraffic has developed 2 different applications compatible with each platform. Depending on your mobile device's operating system (Android, iOS), you should download the MarineTraffic application from the respective store.
Therefore, upon switching from an iOS device (e.g. iPhone) to an android mobile device (and vice versa), you will have to re-download the corresponding app.