For Android 6.0 and greater, please disable battery
optimizations for Share GPS in settings.
You may not have the drivers for your device installed.
If your device came with a software disk, try installing the
software. Otherwise search the net for the drivers for your
device.
Yes, it's a bit complicated. When connecting over USB you
are using a TCP port, and unfortunately, GPS mapping apps
typically only support com ports. Therefore you must use
software to redirect TCP to a virtual com port.
So I had this running over Bluetooth with my mapping program,
then I closed the mapping program and re-opened it but it either
could not open the port, or no data is coming in.
Depending on the bluetooth stack, you may have to
re-establish the connection from the Share GPS app.
On the app, select the Connect option and then find
your PC device in the list. Even if it says Connection
failed, try your connection on the PC again. YMMV.
It appears some GPS units are not providing NMEA string to
the Android SDK. Use the Create NMEA option from settings
to have Share GPS create the NMEA strings from location data.