I have opened a ticket for you on this issue. I'm still not understanding at what point there is a problem. Were you able to add the select list to your checkout page? Did you set a session variable to this posted elements value? Have you updated the server behavior to use this session variable for the service type? There is really not much else to this, you are just getting the value from a variable rather than hard coding it. So long as you have the select list in the checkout form and are setting the value to a session variable you should be able to reference this session variable in the server behavior.