startup.cs

// serve static linked files (JavaScript and CSS for the editor)
app.UseStaticFiles(new StaticFileOptions {
  FileProvider = new Microsoft.Extensions.FileProviders.PhysicalFileProvider(
     System.IO.Path.Combine(System.IO.Path.GetDirectoryName(
        System.Reflection.Assembly.GetEntryAssembly().Location),
        "TXTextControl.Web")),
  RequestPath = "/envelope/create/TXTextControl.Web"
});

app.UseStaticFiles(new StaticFileOptions {
  FileProvider = new Microsoft.Extensions.FileProviders.PhysicalFileProvider(
     System.IO.Path.Combine(System.IO.Path.GetDirectoryName(
        System.Reflection.Assembly.GetEntryAssembly().Location),
        "TXTextControl.Web")),
  RequestPath = "/collaboration/edit/TXTextControl.Web"
});