How do I activate and deactivate item in my invenotory

I need to activate and deactivate item via clicking. Seems like construct runs from top to bottom and sets every time key_active to 0. How I can do that first click it sets key_active to 1 and on second click it sets to 0 ?

You could use an else statement

or

Mouse on key clicked - system set key_active : 1 - key_active

(if key_active is 1 -- 1 - 1 = 0

if key_active is 0 -- 1 - 0 = 1)