What am I doing wrong? COB LED with LED Driver
You have a buck converter that can output a maximum of 32V with 36V supply, but your LED needs 31V typical, the particular sample you have might need more, the data sheet link is broken.

Anyway, the key thing is that a buck converter can only output less than the supply, so it will not light with a 24V supply, and only maybe marginally supply enough even with a 36V supply to regulate well.

The output voltage limit is 30V and see also note 4 (maximum output voltage is input -3V).