confused by file extension(.appx)

aloha999

 What did you put inside the .appx package created with MakeAppx? If you put there the executable to launch your application, all its dependencies and an AppxManifest with the appropriate entries, then your package is as good as an .msix and you don't even need to use the MSIX Packaging Tool. You could submit it to the Store directly as Timothy said.

If you tried to put the installer executable in the .appx package and then convert it with the MSIX Packaging Tool, that will not work. In that case what you would do instead is convert the installer directly with the tool, i.e. put the .exe where you were using the .appx in the packaging tool. You could also use the packaging tool to sign your package when it is created in a single step, instead of calling signtool separately.