servicecall out policy failing with 500 error when the same url is working when provided in target backend

[#1]

Hi ,

I'm using service call out policy to do a HTTPS call in the proxy pre flow. But it is failing with HTTP status code 500. When I use the same url in target backend I'm able to connect it successfully without any issue. Can you please let me know if I'm missing out anything here.

Below is my service call out policy details.

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<ServiceCallout name="ServiceCallOut_request" enabled="true" continueOnError="false" async="true">
    <DisplayName>3servicecallout</DisplayName>
    <Properties/>
    <Request variable="JSONcontent" clearPayload="true">
        <IgnoreUnresolvedVariables>false</IgnoreUnresolvedVariables>
        <Set>
            <Verb>POST</Verb>
            <Payload>{request.content}</Payload>
        </Set>
    </Request>
    <Response>MatchServiceCallResponse</Response>
    <HTTPTargetConnection>
        <URL>https://backend.url</URL>
      </HTTPTargetConnection>
</ServiceCallout>

Before the service call out , I have assign message policy . Below is the assign message policy code.

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<AssignMessage name="AssignMessage_request" enabled="true" continueOnError="false" async="false">
    <DisplayName>AssignMessage_request</DisplayName>
    <AssignTo type="request" transport="http" createNew="false"/>
    <Copy source="request">
        <Payload contentType="application/json" variableSuffix="#" variablePrefix="%">%requestJSONcontent#</Payload>
    </Copy>
    <Set>
        <Path>/pathname</Path>
    </Set>
    <AssignVariable>
        <Name>target.copy.pathsuffix</Name>
        <Value>false</Value>
    </AssignVariable>
    <IgnoreUnresolvedVariables>true</IgnoreUnresolvedVariables>
</AssignMessage>