PHP - Json POST con PHP

<?php

//API Url

$url = 'https://acumbamail.com/api/1/addSubscriber';

//Initiate cURL.

$ch = curl_init($url);

//The JSON data.

$jsonData = array(

    'constumer_id' => 'sssa',

    'auth_token' => 'sdsss',

	'list_id' => 'dsafa',

	'merge_fields[email]' => 'prueba@gmail.com'

);

//Encode the array into JSON.

$jsonDataEncoded = json_encode($jsonData);

//Tell cURL that we want to send a POST request.

curl_setopt($ch, CURLOPT_CUSTOMREQUEST, "POST");

//Attach our encoded JSON string to the POST fields.

curl_setopt($ch, CURLOPT_POSTFIELDS, $jsonDataEncoded);

//Set the content type to application/json

curl_setopt($ch, CURLOPT_HTTPHEADER, array('Content-Type: application/json'));

//Execute the request

curl_exec($ch);

'merge_fields["email"]'

$valor_a_enviar = http_build_query($jsonData);

$ch = curl_init($url);

$resultado = curl_exec($ch);

curl_close($ch);