Mouse up not called on border

I’m using a border element for my fire button in my mobile game (because the basic button doesn’t allow me to move the camera with touch while holding it), inside the mouse down function I’m calling the function to start shooting and on mouse up the function to stop shooting. For some reason when I hold the button and move my finger away from the button the mouse up function is not called of my finger is not above the border.

I tried fixing it by checking which finger tapped the fire button to check when that finger will release but I can’t get it to work.