I bought a cheap USB webcam module on Aliexpress for £7 to monitor my KP3S via MKS Pi and Fluidd. Being just the bare module i had to come up with a way to mount it in a suitable place on the printer. The Kingroon KP3S luckily has a steel base so magnets were the obvious choice, two 5mm dia x 4mm neodimium magnets did the trick. 

The photos are from the fitting, I've added a M3X24 with washers and nut to fix everything together.

aliexpress camera: https://www.aliexpress.com/item/1005004029465825.html?spm=a2g0o.order_list.order_list_main.28.21ef1802xgxGpz