I was trying to remember when I said that as it didnt make sense but I see that it is just an excerpt ... anyway as far as I am aware you cannot "pre-pay" before your interview
Yeah, it's from an excerpt you posted on March 29.
From reading here, you can sometimes pay with cash, sometimes not. Sometimes pay with Credit Card, sometimes not. Sometimes pay with a money order, sometimes not. So paying before-hand would help nullify the stress of preparing for the interview!