how we integrate instamojo with codeigniter - php

Question

I am facing error while saving data in database because webhook(instamojo) url is not working with my code.
How we redirect to webhook page and what is the webhook format for codeigniter framework.
I am using instamojo payment gateway
$ch = curl_init();
curl_setopt($ch, CURLOPT_URL, 'https://test.instamojo.com/api/1.1/payment-requests/');
curl_setopt($ch, CURLOPT_HEADER, FALSE);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, TRUE);
curl_setopt($ch, CURLOPT_FOLLOWLOCATION, TRUE);
curl_setopt($ch, CURLOPT_HTTPHEADER, array("X-Api-Key:test_12345", "X-Auth-Token:test_asbcs"));
$payload = Array(
'purpose' => $username,
'amount' => $this->input->post('amount'),
'phone' => ,
'buyer_name' => $username,
'redirect_url' => 'url',
'send_email' => true,
'webhook' => 'url',
'send_sms' => true,
'email' => $this->input->post('email'),
'allow_repeated_payments' => false,
);
curl_setopt($ch, CURLOPT_POST, true);
curl_setopt($ch, CURLOPT_POSTFIELDS, http_build_query($payload));
$response = curl_exec($ch);
curl_close($ch);
$json_decode = json_decode($response, true);
$long_url = $json_decode['payment_request']['longurl'];
header('Location:'.$long_url);
This is webhook code which I am using in webhook page. Please help me to solve this issue. Thanks in advance
$data = $_POST;
$mac_provided = $data['mac'];
unset($data['mac']);
$ver = explode('.', phpversion());
$major = (int) $ver[0];
$minor = (int) $ver[1];
if($major >= 5 and $minor >= 4){
ksort($data, SORT_STRING | SORT_FLAG_CASE);
} else {
uksort($data, 'strcasecmp');
}
$mac_calculated = hash_hmac("sha1", implode("|", $data), "salt key");
if($mac_provided == $mac_calculated){
if($data['status'] == "Credit"){
database query ---
return true;
} else{
return false;
}
} else{
return false;
}