"NuGet Pack ..." error: The user name or password is incorrect. Where is "NuGet Pack" getting its information from?

While building my C++ application, the postbuild event contains the following command:

NuGet pack "$(ProjectPath)" 
           -OutputDirectory "$(TargetDir)NuGet"
           -IncludeReferencedProjects
           -Properties Configuration=$(ConfigurationName)

First this failed due to error code 9009, meaning it didn't find the program "NuGet.exe". I have downloaded that program on my PC, and now this is the error message I get:

C:\Program Files\Microsoft Visual Studio\2022\Professional>NuGet pack ...
Attempting to build package from '....csproj'.
MSBuild auto-detection: using msbuild version '17.14.23.42201' from 'C:\Program Files\Microsoft Visual Studio\2022\Professional\MSBuild\Current\Bin'.
Packing files from 'C:\...\bin\Debug'.
Using '....ExternalInterface.nuspec' for metadata.
The user name or password is incorrect.

This latter is confirmed by Developer Command Prompt (I get there the same error message).

I have the impression "NuGet.exe" is configured somewhere in order to get username/password from... where?

Here is where I stored "NuGet.exe":

C:\Program Files\NuGet>dir /S /B
C:\Program Files\NuGet\nuget.exe

What can I do now? Should I re-install "NuGet.exe" in some official way?

P.s. by adding detailed verbosity to the "NuGet" command, this is the extra information I get:

The user name or password is incorrect.
System.IO.IOException: The user name or password is incorrect.

   at System.IO.__Error.WinIOError(Int32 errorCode, String maybeFullPath)
   at System.IO.FileSystemEnumerableIterator`1.CommonInit()
   at System.IO.FileSystemEnumerableIterator`1..ctor(String path, String originalUserPath, String searchPattern, SearchOption searchOption, SearchResultHandler`1 resultHandler, Boolean checkHost)
   at System.IO.Directory.GetFiles(String path, String searchPattern, SearchOption searchOption)
   at NuGet.Common.PathResolver.PerformWildcardSearch(String basePath, String searchPath, Boolean includeEmptyDirectories, String& normalizedBasePath)
   at NuGet.Packaging.PackageBuilder.ResolveSearchPattern(String basePath, String searchPath, String targetPath, Boolean includeEmptyDirectories)
   at NuGet.Packaging.PackageBuilder.AddFiles(String basePath, String source, String destination, String exclude)
   at NuGet.Packaging.PackageBuilder.PopulateFiles(String basePath, IEnumerable`1 files)
   at NuGet.CommandLine.ProjectFactory.ProcessNuspec(PackageBuilder builder, String basePath)
   at NuGet.CommandLine.ProjectFactory.CreateBuilder(String basePath, NuGetVersion version, String suffix, Boolean buildIfNeeded, PackageBuilder builder)
   at NuGet.Commands.PackCommandRunner.BuildFromProjectFile(String path)
   at NuGet.CommandLine.PackCommand.ExecuteCommand()
   at NuGet.CommandLine.Command.ExecuteCommandAsync()
   at NuGet.CommandLine.Command.Execute()
   at NuGet.CommandLine.Program.MainCore(String workingDirectory, String[] args, IEnvironmentVariableReader environmentVariableReader)

P.s.2: hereby the contents of the corresponding .nuspec file:

<?xml version="1.0" encoding="utf-8"?>
<package >
  <metadata>
    <id>$id$</id>
    <version>9.10.1680.1</version>
    <title>$title$</title>
    <authors>$author$</authors>
    <owners>$author$</owners>
    <requireLicenseAcceptance>false</requireLicenseAcceptance>
    <icon>Frameworks.png</icon>
    <description>Project description</description>
    <releaseNotes></releaseNotes>
    <copyright>$copyright$</copyright>
    <tags></tags>
    <dependencies>
      <group targetFramework=".NETFramework4.8" />
    </dependencies>
 </metadata>
 <files>
    <file src="\\<FileServer>\Packages\NuGet\icons\" />
  </files>  
</package>

Some thoughts:

1. By adding "detailed" verbosity, I now know that there is a problem while resolving some path.
2. It would be very useful to have actual argument values instead of the general function description, as in the following lines:
   2.1. Replace at System.IO.Directory.GetFiles(String path
   2.2. ... by at System.IO.Directory.GetFiles("C:\..."
3. NuGet Pack /? reveals the -NonInteractive switch. In my opinion this means that NuGet Pack can be used in an interactive way too and this seems to be the default. As a result I expect the question for a username/password. As this question does not appear, I suspect that information to be present in some file, but where? (The .nuspec file seems not to contain any such information and the files, referred to, seem only to be *.ico and *.png files)