I have purchased and downloaded the AIDE Premium key but anytime I try to use it, it says unlock all features if I click on the button it opens up Google play for another payment.
Problem with premium key
The premium key is ancient and outdated that and the UI Designer were brought out long before IAP and subscriptions became a thing on Android. The reason your seeing the dialog for the developer key is because you dont own everything it includes look closely at the dialog to see whats actually included. Its supposed to be the recommended way for new users to unlock features of AIDE its also ment to be a better deal and obviously is less hassle for anyone that wants all features as it doesnt require multiple keys (apps) to be installed.
Basically the developer key (IAP) and the premium key (separate app) are 2 different things, but the premium key should still be working, meaning you should be able to do everything listed in the app description, the app description for the premium key that is.
Okay what if I purchase the developer license would it work.
Your premium key should be fully working even if you are still seeing the puchase dialog for the dev license you should still be able to save files and do everything else included with your premium key. AIDE is kinda dead there doesnt seem to be any official support, the apps very outdated and theres bugs that probably will never be fixed, I would think twice before spending any more money on it.
Can you post a screenshot of the purchase dialog for me its been years since ive seen it (i got the dev license a long time ago) but i cant remember what it unlocks that the premium key doesnt.