Airside is now on simMarket.
If you buy it there you are given a key. Run the installer, type your e-mail address, and put the key in the box under Bought Airside from a marketplace? on the same screen. There is no account to make first and no website to visit.
If you have already tried the free hour on that computer, use the same address. Your key takes over from the demo, on the same licence, and nothing you have done is lost.
Every place Airside is sold is listed on where to buy, and anywhere that is not on that page is not us.
Wherever you bought it, support is ours. Write to support@airsideatc.com.