Error code 80073cf9 when installing my own app from Store
Uninstall the development build from your phone and then you will be able to download the app from Store.
Some interesting facts
Since 8.1 (.appx) you can not install an app from Store if you already have the app installed. This include your development builds deployed from your computer.
Before 8.1 (.xap) you were able to run both your development build and the Store app at the same time. This was since the Store changed the GUID of the app when it was uploaded. For some reason Store doesn't change the GUID of the uploaded app anymore.
I also meet the error 80073CF9. With my case, the reason is the setting of memory location. I reproduced the issue as below: 1. I chose phone memory to install apps 2. Second, I updated the phone from Windows 8.1 to Windows 10. Somehow, I changed to SD card memory to install apps. 3. After upgrading to Windows 10, some apps had to be reinstalled, but the error 80073CF9 raised. At that moment, the phone still used SD card memory to install apps, not the same as the original memory. --> I switch the memory to install apps from SD card to phone (Setting / Storage / Store new apps on my Phone. It's done.
Conclusion with my case: The memory in order to install application has been changed