Is it illegal (state or federal) to purchase a PSA eGift Card using a USPS money order mailed to one of their stores?

I called the Mt. Pleasant store, they would not accept a usps-mo through the mail to be placed on an eGift Card. The purchase of a eGift Card had to either be by using a credit card or coming into the store cash in hand. (I live in the middle of the county so the latter is out and I try to limit credit card use to an absolute minimum). Just seems odd and shouldn't be that big of a deal.

Not illegal, just a business practice.

The post office told me just a week or so ago that there has been a lot of issue's with fake or stolen postal money orders lately so many banks will hold them before cashing.
Im sure PSA is just covering their backsides against this happening to them too. It's the oldest scam in the world, buy gift cards with stolen checks or a stolen credit card number.