Please convert the newest version to apk
Unfortunately, it's impossible to do it differently right now. I upload the apk build through the itch.io uploader, which automatically packs it into a zip archive. If I do it directly, I won't be able to update the current version, i.e., right now you could buy 0.3 and after the update get access to both 0.3.1 and 0.3.1.1. If I upload the apk file directly, as I do with the public version, then each separate version will have to be purchased separately.
I'll write to their tech support, maybe they can help with something.