Do I need to pay a monthly fee in addition to the buying the GPS Tracker?

Yes, you do

To offer you unlimited range and tracking, YoGPS GPS Trackers need a cellular connection to send its location data to your phone. We pay back to back fees to network service providers to provide this cellular connection. The cost of the cellular connection and data transfer is recurring and ongoing. By paying a fixed monthly fee, you are ensuring that you have uninterrupted access to location tracking across many countries including USA, Canada, Mexico, Brazil, Morocco, Egypt, Australia, India and many more.