Do I get a warning message if my parking credit is running low?
Yes, you will receive an e-mail when there is less than € 10,- worth of deposit in your account. If you have too little balance, the barrier will still open when you enter the campus. But then you do will have problems at the exit. The reason you can enter the campus, is that you must have the opportunity to leave the campus for free within 30 minutes, even with a low balance.
Be aware that the email warning offers no guarantee. You might possibly overlook this message or something goes wrong when sending. You are still responsible for having enough deposit in your account.