What is the format of tokens and leads(input json format) used in request campaign rest api? I am getting error code 609 with message Invalid value specified for attribute 'null' .

[SanfordWhiteman]

It is giving me correct output, but can you give something more optimized in accordance with the code.

As long as you're using Java's builder-based approach, it's always going to seem clunky compared to JS or PHP.  There are some libs you can use to allow for all-at-once JSON::stringify, like Gson.​ I can't vouch for any of these.