Ionic / Cordova won't deploy to Windows 10 phone

I have an existing Ionic app that I am trying to test on my Windows 10 mobile phone, but i cannot get Ionic (or Cordova) to deploy to the phone. I have added the Windows platform using ionic platform add windows and then tried to deploy using ionic run windows --device -- --phone --archs="x86" but that results in:

Deploying app package...
Unexpected error from installation:
Error: Not implemented
You may have previously installed the app with an earlier version of cordova-windows.
Ensure the app is uninstalled from the phone and then try to run again.
ERROR: Error: Not implemented

If i do ionic run windows --list to get a list of detected devices i get this:

Available windows devices:
0. Device (device)
Available windows virtual devices:
No devices found matching the specified criteria.

If I try to deploy directly to 0. Device (device) then the app launches on my desktop computer.

Windows itself can "see" my Windows 10 phone and i can browse the contents of it in Windows Explorer.

I have also enabled Developer Mode on the phone so it will load apps from anywhere and I have purchased a Windows Developer License to see if that would help, but it didn't.

Finally, I tried installing the app using the Device Portal feature, but when I try to install it, I get this error:

Failure reason: Failed to start deployment. Failure text: No signature was present in the subject.
 (0x800b0100)

Has anyone else been able to deploy an Ionic / Cordova app to a Windows 10 device? If so, how did you set it up?

I had the same issue. By default the cordova build command produces two packages: Windows 8.1 and Windows Phone 8.1. To upgrade Windows package to version 10 the following configuration setting must be added to configuration file (config.xml).

<preference name="windows-target-version" value="10.0" />

This resolved the issue.