Citrus HTTP custom message using header elements

Question

Click this link to see Error Message I want to send a custom string through header elements Send endpoint.

element name="CustomSting" value="Mycustomessage"

And I need to validate the custom string while in receiving endpoint.

element name="CustomSting" value="Mycustomessage" enter image description here

<template name="REST_Connect_Uri">
    <send endpoint="echoEndpoint">
        <message name="helloMessage">
        <data>Template GET message</data>
        </message>
        <header>
      <element name="citrus_endpoint_uri" value="${Rest_EndPoint_URI}"/>
      <element name="citrus_http_method" value="${Rest_Http_Method}"/>
     <element name="Content-Type" value="${Rest_Content_Type}"/>

     <element name="CustomSting" value="Mycustommessge"/>
        </header>
    </send>
</template>

<template name="REST_Get_Message">
        <receive endpoint="echoEndpoint">
            <message name="helloMessage">     
                <resource file="file:D:/expectedOutput/${OUTPUT}"/> 
            </message>
            <header>
            <element name="CustomSting" value="Mycustommessge"/>
            </header>
        </receive>
</template>