In-App purchases for iPad
 

I can't find details, but it appears you can only purchase prior seasons on the iPhone (which I've done), but not yet on the iPad. Is that correct?

There is no native ipad version, however, you can purchase seasons from an ipad (which is what I have) as the current ipad version is exactly the same as the iphone, only 2x the size.

yes
 

Yes. I have purchased seasons on the iPad. It helps to make sure you have the latest version on the iPad. That gives you the option to purchase on the home page.

I makes no difference if you run iOOTP on the iPhone/iPod or iPad. Even after the Universal update it will not make a difference as it is still the same app.

For buying additional seasons: make sure you have the newest version installed, which is 1.1.2 (to check, open the Credits Screen).

Problem Solved
 

It was a settings issue. The allow in-App purchases button was "off." Thanks t everyone. It's now working properly.

Right, I should have thought about that. We are required to check that (I guess it is a good thing) and disable IAP stuff on our side if the user disables IAP on his device.