Hello.
Thank you for purchasing Juicebox-Pro.
I'm sorry you're having such a poor first experience with Juicebox-Pro, though.
I hope my notes below help to clarify a few things.

This is a known issue and is due to using a version of AIR without support for WebKit (the embedded browser which JuicboxBuilder-Pro uses for the live preview window on the 'Customize' panel).
The solution is to use the most recent version of AIR with WebKit. This is currently AIR v33.1.1.744 which can be downloaded from the foot of the AIR download page here: https://airsdk.harman.com/runtime
Please see this forum post for more details: https://juicebox.net/forum/viewtopic.php?id=5318

Although Adobe no longer supports AIR themselves, AIR is actually still alive and well. Adobe has passed the development of AIR on to a company called Harman. You can check out their website here: https://airsdk.harman.com/
Also, you can check out the AIR development status over on their GitHub site: https://github.com/airsdk/Adobe-Runtime-Support

I'm very sorry about that.
Please let me know what email address you used to contact us and also where you found it (was it in a purchase email or somewhere on our website) so that I can investigate and fix the problem or change the email address if necessary. Thank you.
(We recently had a problem which was noted earlier in the week whereby the support email address on Gumroad receipts was out of date. This was fixed a couple of days ago.)

Once again, I'm sorry that you've had such a rocky start with Juicebox-Pro.
However, Juicebox and AIR are still both supported and using AIR v33.1.1.744 should hopefully resolve your issue with JuiceboxBuilder-Pro. (Just be sure to uninstall any other version of AIR that you might have installed first.)

Please let me know how you get on and if I can be of any further assistance.
Thank you.