namespace Test.ServiceModel
open System
open System.IO
open System.Collections
open System.Collections.Generic
open System.Runtime.Serialization
open ServiceStack
open ServiceStack.DataAnnotations
    [<DataContract>]
    type ScopeType =
        | Global = 1
        | Sale = 2
    [<AllowNullLiteral>]
    type EnumResponse() = 
        member val Operator:ScopeType = new ScopeType() with get,set
    [<AllowNullLiteral>]
    type EnumRequest() = 
        interface IPut
        member val Operator:ScopeType = new ScopeType() with get,set
To override the Content-type in your clients, use the HTTP Accept Header, append the .xml suffix or ?format=xml
The following are sample HTTP requests and responses. The placeholders shown need to be replaced with actual values.
POST /xml/reply/EnumRequest HTTP/1.1 
Host: test.servicestack.net 
Accept: application/xml
Content-Type: application/xml
Content-Length: length
<EnumRequest xmlns:i="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://schemas.datacontract.org/2004/07/Test.ServiceModel">
  <Operator>Global</Operator>
</EnumRequest>
HTTP/1.1 200 OK Content-Type: application/xml Content-Length: length <EnumResponse xmlns:i="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://schemas.datacontract.org/2004/07/Test.ServiceModel"> <Operator>Global</Operator> </EnumResponse>