watch will not charge

First, it may need prolonged charging .Leave it on the charger for half an hour to see if the issue persists. If it persists, try these steps

Make sure that you're using the Apple Magnetic Charging Cable or USB-C Magnetic Fast Charging Cable that came with your Apple Watch.

Make sure that you plug the Apple Magnetic Charging Cable or USB-C Magnetic Fast Charging Cable all the way into the USB Power Adapter, then make sure that you plug the adapter all the way into a power outlet.

If you use a third-party charging stand, use the charging cable that shipped in the box with your Apple Watch.

Completely remove any plastic wrap from both sides of the charger. 

Make sure that the back of your Apple Watch and the magnetic charger are clean.

Reposition the back of your Apple Watch on the charger. When the charger's magnets align correctly with your Apple Watch, a green or yellow lightning bolt  should appear on the watch face.*

Try a different Watch Magnetic Charging Cable or USB-C Magnetic Fast Charging Cable, and a different USB Power Adapter. If your Apple Watch is out of power, you might need to wait a few minutes for the lightning bolt  to appear after you start charging your device. 

If your Apple Watch still won't charge, force it to restart. Press and hold both the side button and Digital Crown for at least 10 seconds, or until the Apple logo appears.