How can I make a UI button's action happen before `Input.GetMouseButtonDown` action in another script?

Hello!

When I click my pause button I call this function

 public void PauseGame()
 {
     fcs.enabled = false;
     Time.timeScale = 0;
     pcs.ActivateCanvas();
     pauseButton.SetActive(false);
 }

fcs is another script and that script uses

 void Update()
 {
     if (Input.GetMouseButtonDown(0))
     {

         spawnPosition = Camera.main.ScreenToWorldPoint(Input.mousePosition);

          //And a bunch of code in here that I don't think matters to spawn a gameobject
     }
 }

When I pause the game I want to deactivate the fcs script, which it does, but in some cases the button is positioned at a possible spawn point for the gameobject in Update which makes it first spawn that object and then pause the game and deactivate the script.

.

I assume this is because the button triggers on ButtonUp but the spawning of gameobjects triggers on ButtonDown but I can't really figure out how to solve this.

.
Does anyone know of a solution to make the button trigger instantly and in that way trigger fcs.enabled = false; before it can spawn a new gameobject (or any other way to solve this)? I've tried adding them to the script execution order list but that did not help.

Appreciate any help, thank you!