I have some files that i need to install in temp directory before the actual installation of the files i am using a custom action in c# which will install the files embedded in my msi in the temp folder of the user.

using System;
using System.Diagnostics;
using System.IO;
using WixToolset.Dtf.WindowsInstaller;

namespace CustomActionVerifyButton
{
    public class CustomActions
    {
        [CustomAction]
        public static ActionResult VerifyOnPremURL(Session session)
        {
            session.Log("Begin Verifying OnPremURL");

            try
            {
                string tempDirectory = session["TEMPFOLDER"];

                session.Log($"ABRACADABARA {tempDirectory}");

                string[] fileKeys = {"RegistrationModule", "ConnectivityCheck"};

                foreach (var fileKey in fileKeys)
                {
                    string sourceFilePath = session.Format($"[# {fileKey}]");
                    string destFilePath = Path.Combine(tempDirectory, Path.GetFileName(sourceFilePath));

                    File.Copy(sourceFilePath, destFilePath, true);

                    session.Log($"Copied {sourceFilePath} to {destFilePath}");
                }

                session.Log("End InstallFilesToTemp");

                return ActionResult.Success;
            }
            catch (Exception ex)
            {
                session.Log($"ERROR in InstallFilesToTemp: {ex.Message}");
                return ActionResult.Failure;
            }

        }
    }
}

when this custom action is called my msi finishes and in the log file i get a error indicating some problem with my custom action.

i have also tried to copy a file from my files in temp folder and it works.

using System;
using System.Diagnostics;
using System.IO;
using System.Xml.Linq;
using WixToolset.Dtf.WindowsInstaller;

namespace CustomActionVerifyButton
{
    public class CustomActions
    {
        [CustomAction]
        public static ActionResult VerifyOnPremURL(Session session)
        {
            session.Log("Begin Verifying OnPremURL");
            Debugger.Launch();

            try
            {
                string tempDirectory = Path.GetTempPath();
                if (!tempDirectory.EndsWith(Path.DirectorySeparatorChar.ToString()))
                {
                    tempDirectory += Path.DirectorySeparatorChar;
                }

                string sourceFilePathReg = @"C:UsersDemoregistration_module.exe"; //session.GetSourcePath("RegistrationModule");
                string sourceFilePathCon = @"C:Usersconnectivity_check.exe"; //session.GetSourcePath("ConnectivityCheck");
                string destFilePathCon = Path.Combine(tempDirectory, "secops_agent_registration_module.exe");
                string destFilePathReg = Path.Combine(tempDirectory, "secops_domain_connectivity_check.exe");

                File.Copy(sourceFilePathReg, destFilePathReg, true);
                File.Copy(sourceFilePathCon, destFilePathCon, true);

                session.Log("End InstallFilesToTemp");

                return ActionResult.Success;
            }
            catch (Exception ex)
            {
                session.Log($"ERROR in InstallFilesToTemp: {ex.Message}");
                return ActionResult.Failure;
            }

        }
    }
}

but when i try to copy the file from the msi it does not work