How to make the POST request and made shown in trace section

[#1]

I want to made the put request and send JSON to my end point and get response. the issue is that I always receive 4xx errors.

Here is my target endpoint, the service endpoint is http://109.166.244.140:9763/webRS/services/user/validateCredentials with POST method. What am i doing wrong? How can i pass JSON and make the POST request? Thank you.

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<TargetEndpoint name="default">
    <Description/>
    <FaultRules/>
    <PreFlow name="PreFlow">
        <Request>
            <Step>
                <Name>GetCredentials</Name>
            </Step>
            <Step>
                <Name>BasicAuthCredentials</Name>
            </Step>
        </Request>
        <Response/>
    </PreFlow>
    <Flows>
        <Flow name="userCredentials">
            <Condition>(proxy.pathsuffix MatchesPath "/validateCredentials") and (request.verb = "POST")</Condition>
            <Description/>
            <Request/>
            <Response/>
        </Flow>
    </Flows>
    <PostFlow name="PostFlow">
        <Request/>
        <Response/>
    </PostFlow>
    <HTTPTargetConnection>
        <Properties/>
        <URL>http://109.166.244.140:9763/webRS/services/user</URL>
    </HTTPTargetConnection>
</TargetEndpoint>