I'm sorry you're having trouble. What device are you trying to download it on? Some common issues are:
-Virus/file scanners preventing the file from downloading
-Not having enough space on your device
-Internet connection issues not allowing you to properly access the file
-An Android device that's too old
-Things now working because you're downloading through the Itch app rather than directly on the site, or the reverse and downloading from the site rather than through the app (the app tends to work on mobile and the site tends to work for laptops).
I hope it's able to work out.