Try downloading it directly from a browser instead of using the app. It looks like the itch.io client can't download unclaimable games with 100% discount.
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Yeh ,Itch is an extremely messy operation.
It's been around a long time now and the owner/s seems incapable of improving the site and / or the client in a major way.
+ Stopping devs from removing games from our libraries.
Me and many others just won't spend too much cash here as it's too unpredictable and chaotic.