Hi, i dont think you can. Check out: https://gettingstarted.mendixcloud.com/link/certification
There may be a different pricing if you are a student.
I know if someone refers you for Mendix the person that got invited will receive a voucher code, which can be used for Mendix Rapid Developer Certification Exam. However, I'm not sure if it will be free or you get a discount. But the amount of discount you get I'm not sure about that.
As far as I remember, they used to give you 10% discount on your Rapid Developer exam when you get invited by someone (not sure if this still applies, but is used to). Perhaps there might be discounts on some events e.g. Mendix-World 2019?
Yes, you need a voucher code to enter free.
If your company work with them, I think you will have a code and you should ask them about what is the code.
They will send you by email and you will register by this code. You will fill the form to register the exam.
They will check your form and after that they will send you confirmation email.
After confirmation email they will send you the exam link.
I hope this info will help.
( if your company doesn’t work with them maybe they will share code who knows :)). I advise you to ask them by email. )