This error indicates a problem in Windows. Nothing I can do about it, sorry.
You might want to check if there are any pending Windows updates or updates in the Microsoft Store.
I can only offer a refund of your purchase.
And as I said before, you should be able to buy the app through the Microsoft store. If that doesn't work either, I would consider reinstalling Windows (or upgrading to Windows 11)
Edit: I was googling the error and found this: https://techcommunity.microsoft.com/t5/msix/error-parsing-app-package/m-p/3036896/highlight/true#M2503
Maybe you firewall or something is blocking the AppInstaller from accessing the installation files which are located on my server