How to register Iris recognition in Galaxy S8/S8+?

Keep your eyes fully open and look at the top of the screen. Iris  recognition may not work properly in direct sunlight. For best results, avoid direct sunlight and perform this process indoors.

And, keep the camera clean as dirt and debris on the iris camera, LED sensor, or proximity sensor may cause the device to have difficulty recognizing your irises. Position your eyes inside the circles on the screen. The iris recognition camera will scan your irises.