files upload WCF C# web service

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C#

WCF

File-Upload

webservice

i am working in uploading files with WCF web service,
here's my code for uploading

public string UploadTransactionsFile(string uploadPath)
           {
               string uploadTransactionsFile;

               if (String.IsNullOrEmpty(uploadPath))
                   return string.Empty;

               if (!ValidateTransactionsFile(uploadPath))
                   return string.Empty;

               try
               {
                   var dir = @"C:\Upload\";
                   string myUploadPath = dir;
                   var myFileName = Path.GetFileName(uploadPath);
                   CheckDirectory(myUploadPath);

                   var client = new WebClient { Credentials = CredentialCache.DefaultCredentials };

                  client.UploadFile(myUploadPath + myFileName, "PUT", uploadPath);
                   client.Dispose();


                   uploadTransactionsFile = "ok";
               }
               catch (Exception ex)
               {
                   uploadTransactionsFile = ex.Message;
               }

               return uploadTransactionsFile;
           }

i create a windows form as a test client and add the service reference,

my code in calling the method and hardcoded the file i want to upload:

private testServiceClient testService;
     private void Button_Click(object sender, RoutedEventArgs e)
            {
                var File = "C:\\file.csv";
                testService = new testServiceClient();
    
                testService.UploadTransactionFile(File);
    
            }

i can upload files using one computer, but when i put my test client to another computer,
i can't, because the file is just passing the stringpath, which will cannot find in server computer.

am i missing something? help me pls, do i have to send my file as byte[]? how to do this?