Is there a way for me to be able to only check for a single button press?

Basically, at the moment I have
btnBrushUpgrade.onClick.AddListener(buyDogBrush);
In my update function, though whenever I click the button it buys as many as it possibly can because its checking every frame. The image is attached thanks

Im an idiot, put it in the start function facepalm

Thanks guys lol