What am I missing?

[DreadyE]

Hey guys and girls,

Love this puzzle but I tried a couple now but and every time I end up with 3 left in the grey.
What am Ì missing? How to solve this using logic? Or is there no way and I will just have to try randomly and see what works? I mean I can do that but for me that is not a nice way to solve this puzzle tbh.

It feels like there is a rule I am missing.

[deantestines]

The way I do it is plug in a number and see if it creates anything impossible (aka if it adds to numbers that are already in the white) and if it does I know its not that one. It's a process of elimination from that point, which could be considered a guessing game.