1. Unscrew the tail cap and remove the battery from the light. Take a look inside the battery chamber and the positive end of the battery. The factory often adds a white paper disc between the battery and the light. This disc needs to be removed prior to using/charging the light.
2. Install the battery with its positive end toward the front of the light.
3. Rotate the switch. Does the OLED screen display any information? 
4. Connect the charging cable with its USB-C end to the flashlight and USB-A end to a power adapter. Does the OLED screen display any message such as progressive arrows and battery percentage?
5. Rotate the switch again when the charging cable is connected. Does the OLED screen display anything? Does the light turn on at the low setting?