I had problems too. I would get an error after submitting my info when it redirected me to PayPal to pay.
I figured out that above the reg form is a place I needed to click on whether I was a vet or etc.
it had looked to me like a price list, not a place to take an action.
After clicking on the right category for me then scrolling down to once again fill in the form to submit it finally did work.
Chris H in CA 2021