Anker didn’t check with me on delivery address so I’m not united with my (generous) gift, but I do own a 10000 PD and a 10000 PD Slim.
The 10000 PD Slim does NOT charge of an IQ3 charger, but it does charge off a PD charger. If I connect 10000 PD Slim to IQ3 a green light comes on then all lights off.
I also noticed some Anker Type C cables have short connector and finnicky to work reliably.
So if charging is slow, ensure it is connected to a 18W PD charger, not IQ3 charger and try different cable.