Just bought a card 0 fees, actual face value of card. Used it to pay a cable bill with no issues.
You don't actually get a card number, you get an activation code and have to go to
https://MyPrepaidCenter.com/redeem to activate it.
Spit out a Master Card with an expiration date 6 months out and all the other info.
If that works online, I can think of a few uses. Does it also work for websites outside US?
At a *guess* they are probably getting some of the % of the sales to run it though and are making their money that way.
OR like your local drug dealer they are keeping it free to start, once they get you hooked then it's gonna cost you.
Or both

Try using Tor with a US exit node.
I tried, but it brings me to
https://www.bitrefill.com/api/cart?redirect showing this:
message "This product does not exist"
status "invalid_product"
I haven't tried a VPN yet.