How Can I change a toolbar icon in a safari app extension at runtime?

I have found this in the documentation.

https://developer.apple.com/documentation/safariservices/sfsafaritoolbaritem

which lead me to be able to use the window variable in the toolbarItemClicked function to get a reference to the toolbar item like so.

var toolbaritemretrieved = false
window.getToolbarItem { (item) in
            toolbaritem = item! as SFSafariToolbarItem;
            toolbaritemretrieved = true;
        }

once I had a reference to the toolbar item I could then run this code and supposedly change the image of the icon.

let path = Bundle.main.path(forResource: "newIcon", ofType: "png")!;
let icon = NSImage(path);
while(!toolbaritemretrieved){
                        //wait for toolbar item to be retrieved
                    }
                    toolbaritem?.setImage(icon);
                    SFSafariApplication.setToolbarItemsNeedUpdate();

However this doesn't work. There are no visible errors but for some reason the icon does not display the new image.

Okay it turns out that there was actually nothing wrong with my code at this point and I had a forgotten breakpoint.