Since the recent changes (requirement to book one hour-based time slot for a day) the script instead just books all available time slots offered (no matter which day or time) although this is normally not possible using the website. Using the website you receive a notification "Sie sind bereits für einen anderen Kurs eingetragen". Maybe it is possible that the script only books the timeslot in which the crone job executes (e.g. executing at 4 pm it books the time slot 4 pm to 8 pm).
Since the recent changes (requirement to book one hour-based time slot for a day) the script instead just books all available time slots offered (no matter which day or time) although this is normally not possible using the website. Using the website you receive a notification "Sie sind bereits für einen anderen Kurs eingetragen". Maybe it is possible that the script only books the timeslot in which the crone job executes (e.g. executing at 4 pm it books the time slot 4 pm to 8 pm).