If you bought it from anywhere other than Samsung or major retailer that sells actual Samsung accessories its likely a fake. A lot of places sell ones that are compatible and will function as a pen but they don't have Bluetooth.
Bluetooth devices give you tons of flexibility, and the S Pen on Galaxy Note phones are Bluetooth compatible! This includes the Note20 5G and Note20 Ultra 5G, which include the most streamlined and customizable S Pens yet. The S Pen is no normal pen and it doesn’t use normal Bluetooth. It's a special kind of BT that will let you pair, charge, and reset the Note's innovative S Pen. Give this link a try: