paygate payweb3 integration in php website - php

Question

I am trying to integrate paygate payment gateway integration into my PHP API. I have gone through their documentation but it is not clear for me. There were three endpoints
initiate
return
query
I don't which endpoint to use. Now I am using initiate endpoint, but when testing in postman I am getting an error
ERROR=DATA_CHK error
Can anyone guide me to sort this out...
public function subscription(Request $request) {
$validator = Validator::make(
$request->all(),
array(
'subscription' => 'required|integer',
'email' => 'required|exists:users,email',
'amount' => 'required|integer',
'payment_mode' => 'required|integer',
),
array(
'exists' => 'The :attribute doesn\'t exists',
)
);
if ($validator->fails()) {
$error_messages = implode(',', $validator->messages()->all());
$response_array = array('success' => false, 'error' => Helper::get_error_message(101), 'error_code' => 101, 'error_messages'=>$error_messages);
} else {
$encryptionKey = 'AQ2Uted8BidhkIEv6oYgrqwS';
$data = array(
'PAYGATE_ID' => 1039433100014,
'REFERENCE' => 'pgtest_123456789',
'AMOUNT' => 3299,
'CURRENCY' => 'ZAR',
'RETURN_URL' => 'http://localhost/avvata/public/home',
'TRANSACTION_DATE' => date('Y-m-d H:i:s'),
'LOCALE' => 'en-za',
'COUNTRY' => 'ZAF',
'EMAIL' => $request->email,
);
$checksum = md5(implode('', $data) . $encryptionKey);
$data['CHECKSUM'] = $checksum;
$fieldsString = http_build_query($data);
//open connection
$ch = curl_init();
//set the url, number of POST vars, POST data
curl_setopt($ch, CURLOPT_URL, 'https://secure.paygate.co.za/payweb3/initiate.trans');
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
curl_setopt($ch, CURLOPT_NOBODY, false);
curl_setopt($ch, CURLOPT_REFERER, $_SERVER['HTTP_HOST']);
curl_setopt($ch, CURLOPT_POST, true);
curl_setopt($ch, CURLOPT_POSTFIELDS, $fieldsString);
//execute post
$result = curl_exec($ch);
echo $result;
exit();
//close connection
curl_close($ch);
}`
Thanks in advance :-)