This may be due to the fact that the quality of the video or audio is not sufficient. Make sure that the location from where you start the verification has a stable internet connection and is sufficiently illuminated. There shouldn't be too much background noise either. It is also important to mention that you must do the identification on your own, i.e. assistance by another person is not allowed.
If it still doesn't work, restart the app or delete it completely and reinstall it. The process should then restart. If this is not the case, contact us via Chat or Phone.