Webservice not showing input fields

I have developed a webservice. Locally it works fine. But as soon as I put it online, the button which I can click when testing locally is not shown...

See here:
ticketez  .nl /scanticket.asmx?op=HelloWorld

My webservice:
<WebMethod()> _
    Public Function HelloWorld() As String
        Return "Hello World"
    End Function


What is going on?

...