Make sure you are using the adapter that came with the package.
Check the Snap Charger: it should be attached to the back of the Smarthandle. The logo should be upside down, and the magnet should click to make sure it is attached this way. Here is a photo as an example.
NOTE: currently, there is only one way to charge the device. Connecting the Snap Charger any other way despite the magnet clicking would not charge the device.
Here is a video instruction on how to use the Snap Charger.