To properly charge your Woojer Vest 4, please make sure to utilize the provided Power Delivery charger (wall charging block), and make sure it is plugged into the USB-C port located on the BACK of your Vest 4.
The LED should be blinking red while with low battery, then gradually filling the LED ring from red, through orange, and then green when fully charged.
You can refer to the following image to see where your Vest's USB-C charging port is located:
