Are you using the Garmin cable? I find mine infuriating and the connection is even worse using a generic cable - which makes no sense to me.
USB cables come in two flavours - power only, or power & data.
You need a data cable in order to mount anything over USB.
I forgot this recently, and ended up stripping wires & soldering stuff before I remembered.
@NotThamesWater started
London Fixed Gear and Single-Speed is a community of predominantly fixed gear and single-speed cyclists in and around London, UK.
This site is supported almost exclusively by donations. Please consider donating a small amount regularly.
Are you using the Garmin cable? I find mine infuriating and the connection is even worse using a generic cable - which makes no sense to me.