I got the charger but it's losing charge and only says fast charger. Doesn't seem to work with the FeIf I needed my phone to charge quicker than 2 hours I would use a corded charger, not wireless. My Intoval Wireless Charger can charge my S21 Ultra, a watch and Buds. I just set my phone on the charger when I go to bed and it is fully charged by the next morning. I usually get 2-3 days out of a charge anyway, so there's never any hurry to charge it fast.
Do you have the old or new Samsung wireless charger duo? The old one is only 9 W. You'll need the new one to get 15 W.