How to add flow variables to JSON payload

[#1]

I have extracted some query parameters and URI path parameters in request flow. I want to add these variables to the request payload.I have extracted using Extract Variable Policy. How to add these to my JSON request payload?

My Extract Variable Policy is:

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<ExtractVariables async="false" continueOnError="false" enabled="true" name="EV-GetStartDate">
    <DisplayName>EV-GetPathType</DisplayName>
    <URIPath name="index" type="string">
        <Pattern ignoreCase="true">/{index}</Pattern>
    </URIPath>
    <QueryParam name="type" type="string">
        <Pattern ignoreCase="true">{type}</Pattern>
    </QueryParam>
    <VariablePrefix>queryinfo</VariablePrefix>
    <IgnoreUnresolvedVariables>true</IgnoreUnresolvedVariables>
</ExtractVariables>