How to query Github GraphQL API from PHP script?

I am querying Github API for some internal monitoring interface. I came across the new GraphQL implementation in the documentation and decided to use it for my interface.

Accordingly, I prepared this small PHP script to test the Github GraphQL API which I have pasted below. I always get ‘Problems parsing JSON’ error whenever I run the script. Am I doing something wrong here? Can somebody help me highlight any mistake I am doing?

<?php
    //GRAPHQL request
    $postData =<<<‘JSON’
    {
    “query”: query{
    user(login:“tojochacko”) {
    name
    }
    }
    }
    JSON;

    $json = json_encode($postData);

    $chObj = curl_init();
    curl_setopt($chObj, CURLOPT_URL, ‘https://api.github.com/graphql’);
    curl_setopt($chObj, CURLOPT_RETURNTRANSFER, true);
    curl_setopt($chObj, CURLOPT_CUSTOMREQUEST, ‘POST’);
    curl_setopt($chObj, CURLOPT_POSTFIELDS, $json);
    curl_setopt($chObj, CURLOPT_HEADER, true);
    curl_setopt($chObj, CURLOPT_VERBOSE, true);
    curl_setopt($chObj, CURLOPT_HTTPHEADER,
    array(
    ‘User-Agent: PHP Script’,
    ‘Content-Type: application/json’,
    'Authorization: bearer '.GITHUB_TOKEN
    )
    );

    $response = curl_exec($chObj);
    echo $response;
?>