how much can a floor be out of level for the leveling pad not to work

There is no specific maximum out-of-level measurement published for the Bootz Pro-Fit leveling pad, but it is designed to work only when it has full, even contact with the subfloor. In general, the floor should be very close to level, with only minor variations that can be corrected using small shims. If the floor is significantly uneven, the leveling pad will not function properly, and the floor will need to be leveled first or a mortar bed used to ensure proper support and prevent issues with the tub.