This is because you clicked the uploadhaven link from a different source other than SteamUnlocked. You must download the game from the original SteamUnlocked/LinksUnlocked site. Copying &Pasting the download link directly will also lead to this error.
Make sure you are also not using the Brave browser. For some reason, Brave doesn’t properly handle referrer settings, so UploadHaven doesn’t know where the users came from.