How to execute multiple exe files from UWP app?

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C#

Windows

UWP

I have 2 exe that are build from C a.exe and b.exe. These exe files are called from UWP app.

What I have tried:

Below is what I did.
I added Windows Desktop Extensions for the UWP
I added 2 folders groubA & groubB in project's root directory then rename a.exe to app.exe and add to groupA folder, rename b.exe then add to groupB folder.
 
In Package.appxmanifest:
<pre><Applications>
      ...
      <Extensions>
        <desktop:Extension Category="windows.fullTrustProcess" Executable="app.exe">
          <desktop:FullTrustProcess>
            <desktop:ParameterGroup GroupId="groupA" Parameters="/groupA"/>
            <desktop:ParameterGroup GroupId="groupB" Parameters="/groupB"/>
          </desktop:FullTrustProcess>
        </desktop:Extension>
      </Extensions>
    </Application>
  </Applications>

In Main class :

await FullTrustProcessLauncher.LaunchFullTrustProcessForCurrentAppAsync("groupA");

to call exe file in groupA folder. When I run UWP app I got error :

windows can not find ...\Appx\app.exe

.
In my understanding, tag <desktop:extension> indicates that app.exe is register as a fullTrustProcess. And <desktop:ParameterGroup GroupId="groupA" Parameters="/groupA"/> indicates that app.exe with groupId ="groupA" and in folder groupA will be executed when LaunchFullTrustProcessForCurrentAppAsync("groupA") is called. Am i right?
Please help me find what wrong here?