System.Nullreferenceexception

Question

There is a webservice that I need to create which needs to have some particularities, among them, the information of Soapaction (as below). However, when I put and will debug I already get the error when testing the contents of the variable "orderID", returns:

System.Nullreferenceexception: 'Undefined object reference for an instance of an object. ' ==> confirmPaymentRequest was Nothing)

When I shoot the Soapaction works, but the customer fails to consume because it returns the following error:

System.Web.Services.Protocols.Soapexception: The server did not recognize the value of the HTTP header Soapaction: confirmPayment.

I don’t know what else to do, given the very little experience in Ws.

Below follows the method:

<WebMethod()>
    <SoapDocumentMethod(Action:="confirmPayment")>
    Public Function confirmPayment(ByVal confirmPaymentRequest As ps.confirmPaymentRequest) As ps.confirmPaymentResponse

        Dim retorno As New ps.confirmPaymentResponse()
        Dim orderID As String = confirmPaymentRequest.orderId
        Dim status As String = confirmPaymentRequest.status
        sql = "insert into ws_payment (orderid, status) values ('" & orderID & "','" & status & "')"
        txtExec = bco.exec(clsRetAcesso.acesso(homologacao, "dbWS"), sql)
        If txtExec <> "OK" Then
            retorno.success = False
            My.Computer.FileSystem.WriteAllText(LocalLog, Date.Now & " - 0030 - Erro: " & txtExec & vbNewLine & "SQL: " & sql & vbNewLine, True)
        Else
            retorno.success = True
        End If
        Return retorno
    End Function

'------------------------------------------------
'