Please check the following:
1) USB charging cord is connected to a working USB outlet.
2) The tracker device is properly connected to the charging cord unit, meaning the contact points on the back of the device should meet the ones on the charging cord unit.
3) Check the contact points on the back of your device to make sure the small openings are free of dust and particle build-up, which could possibly interrupt the connection of your device with the charging cord. We suggest cleaning the back of your device with a cotton swab and a little household (isopropyl) rubbing alcohol. Be sure your charging unit cord connections are clean as well and try charging again.
When properly connected, the tracker face will indicate the unit is in charging mode.
If the troubleshooting steps do not work, please submit a ticket to Amazfit Support here.