Self leveling compound can be used on any surface, including brick, to give the new flooring a flat surface to be installed upon. Leveling compound is used to level an old floor or subfloor, before installing new flooring. Any low place or dip in the floor greater than 1/4 inch should be leveled, to prevent damage to the new flooring.
Self leveling compound is a great deal like concrete, and dries to a very hard surface. Always use a trowel or very large plasterer's blade to smooth it, as you go and check for level. Prime the area where the leveling compound will be used.