4D Paint | Painting | Paint Brush | Multi Channel Painting
For normal map painting to work the image in the source materials normal map channel must also be a normal map. The brush projects the paint from the source to the destination. This means you can NOT use a greyscale image as your normal map source and expect to get a proper normal map in the resulting image. You should also make sure that the destination image is an RGB image and not a greyscale image.