Content Type application/soap+xml; charset=utf-8 was not supported by service

I run into naming problem. Service name has to be exactly name of your implementation. If mismatched, it uses by default basicHttpBinding resulting in text/xml content type.

Name of your class is on two places - SVC markup and CS file.

Check endpoint contract too - again exact name of your interface, nothing more. I've added assembly name which just can't be there.

<service name="MyNamespace.MyService">
    <endpoint address="" binding="wsHttpBinding" contract="MyNamespace.IMyService" />
    <endpoint address="mex" binding="mexHttpBinding" contract="IMetadataExchange"/>
  </service>

Here is the example of a web.config that solve the issue for me. Pay attention on the <binding name="TransportSecurity" messageEncoding="Text" textEncoding="utf-8">

In my case one of the classes didn't have a default constructor - and class without default constructor can't be serialized.

I had the same problem, got it working by "binding" de service with the service behaviour by doing this :

Gave a name to the behaviour

<serviceBehaviors>
        <behavior name="YourBehaviourNameHere">

And making a reference to your behaviour in your service

<services>
  <service name="WCFTradeLibrary.TradeService" behaviorConfiguration="YourBehaviourNameHere">

The whole thing would be :

<?xml version="1.0" encoding="utf-8" ?>
<configuration>

  <system.web>
    <compilation debug="true" />
  </system.web>
  <!-- When deploying the service library project, the content of the config file must be added to the host's 
  app.config file. System.Configuration does not support config files for libraries. -->
  <system.serviceModel>
    <bindings>
      <basicHttpBinding>
        <binding name="basicHttp" allowCookies="true"
                 maxReceivedMessageSize="20000000"
                 maxBufferSize="20000000"
                 maxBufferPoolSize="20000000">
          <readerQuotas maxDepth="32"
               maxArrayLength="200000000"
               maxStringContentLength="200000000"/>
        </binding>
      </basicHttpBinding>
    </bindings>
    <services>
     <service name="WCFTradeLibrary.TradeService" behaviourConfiguration="YourBehaviourNameHere">
        <endpoint address="" binding="basicHttpBinding" bindingConfiguration="basicHttp" contract="WCFTradeLibrary.ITradeService">          
         </endpoint>
     </service>
    </services>
    <behaviors>
      <serviceBehaviors>
        <behavior name="YourBehaviourNameHere">
          <!-- To avoid disclosing metadata information, 
          set the value below to false and remove the metadata endpoint above before deployment -->
          <serviceMetadata httpGetEnabled="true"/>
          <!-- To receive exception details in faul`enter code here`ts for debugging purposes, 
          set the value below to true.  Set to false before deployment 
          to avoid disclosing exception info`enter code here`rmation -->
          <serviceDebug includeExceptionDetailInFaults="true" />
        </behavior>
      </serviceBehaviors>
    </behaviors>
  </system.serviceModel>

</configuration>

As suggested by others this happens due to service client mismatch.

I ran into the same problem, when was debugging got to know that there is a mismatch in the binding. Instead of WSHTTPBinding I was referring to BasicHttpBinding. In my case I am referring both BasicHttp and WsHttp. I was dynamically assigning the binding based on the reference. So check your service constructor as shown below

Refer this image