When you are creating materials in Unreal engine sometimes you can come across elements of the material that are indented as opposed to protruding – or vice versa.

This can be easily fixed with one click of a tick box in the normal map settings. Go to the normal texture and then in its settings tick the box that says ‘Flip Green Channel’ (shown in image). This will invert the normal and hopefully, should fix any issues regarding inverted normals appearing in the wrong direction.