How to write json post in this given sample CURL module - php

Question

i am trying to implement interswitchng.com api. following code is generated from postman's generate code features. When i try to change following status value with dynamic value using php then it shows some error. i think i do some mistake in CURLOPT_POSTFIELDS. So can you suggest me that how can i write this array in CURLOPT_POSTFIELDS ?
<?php
$curl = curl_init();
curl_setopt_array($curl, array(
CURLOPT_URL => "https://sandbox.interswitchng.com/api/v1/quickteller/fundsTransfer",
CURLOPT_RETURNTRANSFER => true,
CURLOPT_ENCODING => "",
CURLOPT_MAXREDIRS => 10,
CURLOPT_TIMEOUT => 30,
CURLOPT_HTTP_VERSION => CURL_HTTP_VERSION_1_1,
CURLOPT_CUSTOMREQUEST => "POST",
CURLOPT_POSTFIELDS => "{\r\n \"mac\": \"8285b03723393d92c30b31474689bc835e448a34345324339e1aef2d0a1a03a438f934a177e0515459e0b6eb6c0c7f3d9a9e26ec3e4447a664343455\",\r\n \"beneficiary\": {\r\n \"lastname\": \"Anari\",\r\n \"othernames\": \"Sammy\"\r\n },\r\n \"initiatingEntityCode\": \"XXT\",\r\n \"initiation\": {\r\n \"amount\": \"100000\",\r\n \"channel\": \"7\",\r\n \"currencyCode\": \"566\",\r\n \"paymentMethodCode\": \"CA\"\r\n },\r\n \"sender\": {\r\n \"email\": \"simon.mokhele#hellogroup.co.za\",\r\n \"lastname\": \"Testing\",\r\n \"othernames\": \"Test\",\r\n \"phone\": \"0732246413\"\r\n },\r\n \"termination\": {\r\n \"accountReceivable\": {\r\n \"accountNumber\": \"0014261063\",\r\n \"accountType\": \"10\"\r\n },\r\n \"amount\": \"100000\",\r\n \"countryCode\": \"NG\",\r\n \"currencyCode\": \"566\",\r\n \"entityCode\": \"058\",\r\n \"paymentMethodCode\": \"AC\"\r\n },\r\n \"transferCode\": \"27205265080\"\r\n}",
CURLOPT_HTTPHEADER => array(
"authorization: InterswitchAuth SUtJQUI2MzQ0OTlFQjk434adsfdfsdf23zNjkzQTcyODRDQ0EzNDY=",
"cache-control: no-cache",
"content-type: text/html",
"nonce: 6fb704016f989a763453456347777",
"signature: +GWrb0434543345gg=",
"signaturemethod: SHA1",
"terminalid: 2vXP0434",
"timestamp: 3343424"
),
));
$response = curl_exec($curl);
$err = curl_error($curl);
curl_close($curl);
if ($err) {
echo "cURL Error #:" . $err;
} else {
echo $response;
}
If i try to use following sentence, then it does not seem proper (i think).
CURLOPT_POSTFIELDS => json_encode($data['postdata']),
Above $data has been send using following code :
$postdata=array( "mac"=>"$maccode", "beneficiary"=>array("lastname"=>"$receiverlastname","othernames"=>"$receiverothernames"), "initiatingEntityCode"=>"$InstitutionCode", "initiation"=>array( "amount"=>"$initiation_amount", "channel"=>"7", "initiation_currencyCode"=>"556", "initiation_paymentMethodCode"=>"$initiation_paymentMethodCode" ), "sender"=>array("email"=>"$senderemail","lastname"=>"$senderlastname","othernames"=>"$senderothername","phone"=>"$senderphone"), "termination"=> array(
"accountReceivable"=>array("accountNumber"=>"0014261063","accountType"=>"10"),
"amount"=>"$to_amount",
"countryCode"=>"$to_countryCode",
"currencyCode"=>"$to_currencyCode",
"entityCode"=>"$to_entityCode",
"paymentMethodCode"=>"$to_paymentMethodCode"
), "transferCode"=>"$transferCode" );
$data=array("url"=>"$url", "header"=>array("Authorization"=>"InterswitchAuth $Authorization","Signature"=>"$signature","Nonce"=>"$Nonce","Timestamp"=>"$timestamp","SignatureMethod"=>"SHA1","TerminalId"=>"2vXP0434"), "postdata"=>$postdata );