How to make transfer data to post query string in json format

I try to make data transfer from first post request (response from it in json) to second (request in second method in multiform/data type, but query param contain Json array).

I need to past value like "4e2c056931d398831128ad2c6a45ec91" in second post request as querystring param mediaIds: [{"mediaId":"54a985e73f0f9360039750aac89d0133","type":0}] where "type":0 just static parameter.

How can I do it? Can I do it via target request? Or I must use "Property expansion"? or maybe it is impossible without Groovy?

P.S. I haven't any problem with parse response from first request, but I don't know how to transform it in json array that I need =(