You need a metadata endpoint for your service, here`s an example.
<services>
<service name="MyService" behaviorConfiguration="MEX">
<endpoint
address="http://localhost:8000/MEX"
binding="mexHttpBinding"
contract="IMetadataExchange"
/>
</service>
</services>
<behaviors>
<serviceBehaviors>
<behavior name="MEX">
<serviceMetadata/>
</behavior>
</serviceBehaviors>
</behaviors>