How to purchase the certification exams ?

Hi Team,

I'm looking for the RHCSA certification exam and when I tried to purchase, the system ask me to provide purchase order or training unit which I'm not aware of.

additionally, I have learned by myself as I have 8 years of Linux experience. therefore, I'm not looking for training or buying any books. just let me sit for the exam and I'm willing to pay for it. why this is not simple and straight forward option please ?

appreciate your assistance on this.