Problem seems to be solved. After hours of looking after the project files, I tried to upload my application to the Appstore directly: • My first and numerous tries were made like this in Organizer: Distribute App -> Custom -> App Store Connect all these tries had the problem • I managed today another way: Distribute App -> TestFlight & App Store This route succeeded at first try and my build is now available in App Store Connect… A bug in Xcode 15?

Corrected. I had forgotten to update the - (BOOL)panel:(id)sender shouldEnableURL:(NSURL *)url method to manage UT types instead of UTI strings

UPDATE: In fact, to the contrary of what I wrote, I can't even read files setting myPanel.allowOtherFileTypes to TRUE

Thanks for your reply. So, there is no way, in a sandboxed app, to perform an extension check? It's a pity as it denies to the app the right to prevent a user typo. In this case, no other compatible application will be able to open the file directly, unless the user corrects itself the extension in the Finder… What I don't understand it that this code works in one of my classes… So why are the Sandbox rules considered as violated in a class, and not in another class using the same code?