How Does DNS Work with Keap Max Classic?

So, do all customers need to go to an Infusionsoft.com link in order to purchase? Or is it possible to brand the cart with a custom Domain name? Based on all I’ve seen, this isn’t possible. Please look at the drawing below and confirm that the middle step always needs to be infusionsoft.com. Is that correct? Or, is it possible to keep my domain name during purchase?