Please try these options to resolve the issue:
- check the GPS settings on your device: Settings > turn Location Services on and enable it for this app (choose 'While Using' option);
- go to the app Home screen, tap Start > Begin > Settings icon in the upper right corner > turn GPS on and select 'Outdoor' mode;
- you may need to wait for a couple of minutes to get the signal since GPS depends on the weather;
- before starting your walk make sure that the signal is ok and at least one GPS indicator is shown on the screen.