Perhaps you can help other users.
There is the “good” old Windows Store error 0x80073CF9. This error was born together with the Windows Phone itself and prevents the installation of apps on the phone. This error comes and goes.
I never got a meaningful answer from Microsoft, how to fix this. There are some hints in the internet, to set the installation target from SD-card to the internal memory. But phones without an SD-card get this error too.
Do you got this error too and solved it for you? How?