How Does Radio Know I Paid For S/W Upgrade?

So I have one of the original Flex 6500s. It worked perfectly up through S/W v2.9x. After that it always got file transfer error when trying to upgrade. I would just downgrade to v2.9x and everything worked. I thought maybe the newer 3.0 versions might have something to offer so I purchased an upgrade, When I try to use it I get a screen to buy the upgrade, which I did. Now when I try to upgrade the radio, I get the same purchase screen but no field or anything else to enter my receipt or license number, just another chance to spend another $200.00+. So, logically, I tried to downgrade the radio back to v2.9 like i did in the past. But.. not I get the file error on that version and have no working radio at all. What happened to flex?