How to invoke a webservice with complex or non-primitive

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VB

ASP.NET

webservice

Hi All.
I got a problem here. How to invoke a webservice with complex or non-primitive parameters in ASP.NET/VB.Net.
I have created a webservice but I can't seem to invoke the methods simply bcoz the codes are complex or are of non-primitive parameters. The following message appears:

The test form is only available for methods with primitive types as parameters.

How do I go about it?
Many thanks.

This is the complex code.

<WebMethod()> _
        Public Function WatchListWS(ByVal strName As String) As WatchListIntResp
        Dim watchStatus As String = ""
        Dim resp As New WatchListIntResp
        Dim objWatchList As Object = Server.CreateObject("VREMIT.Enterprise.ComWatchList")

        Try
            watchStatus = objWatchList.mtdMatchExact(strName, g_global_region_code)

            If watchStatus <> "" Then
                resp.watchlistIntCode = "3"
                resp.watchlistIntMsg = "Hit International"
                'strResult = "3 | Hit International "
            Else
                'strResult = " 0 | Not Watched "
                resp.watchlistIntCode = "0"
                resp.watchlistIntMsg = "Not Watched"
            End If
            Return resp

        Catch ex As Exception
            Return Nothing
        End Try
    End Function