Cross Platform Encoding of Encrypted Strings in PHP and OSX - php

Question

Im encrypting a string in PHP using the following code
<?php
$key256 = "323";
$iv128 = "2424";
$text = "ABC";
$blocksize = 16;
$len = strlen($text);
$pad = $blocksize - ($len % $blocksize);
$text .= str_repeat("0", $pad);
$cipher = mcrypt_encrypt(MCRYPT_RIJNDAEL_128, $key256, $text, MCRYPT_MODE_CBC, $iv128);
echo $cipher;
?>
In SWIFT I use POST Request and get the data from the server and print out the fetched data to the console like this
var request = URLRequest(url: URL(string: "http://www.example.com/test.php")!)
request.httpMethod = "POST"
let akey:String = txt_key.stringValue;
let email:String = txt_email.stringValue
let VAL:String="test"
var data="blah"
let postString = data
request.httpBody = postString.data(using: .utf8)
let task = URLSession.shared.dataTask(with: request) { data, response, error in
guard let data = data, error == nil else { // check for fundamental networking error
print("error=\(error)")
return
}
if let httpStatus = response as? HTTPURLResponse, httpStatus.statusCode != 200 { // check for http errors
print("statusCode should be 200, but is \(httpStatus.statusCode)")
print("response = \(response)")
}
let responseString = String(data: data, encoding: .utf8)
print(responseString)
}
task.resume()
This keeps printing nil even when the Web Browser shows the encrypted string.
What I'm I doing wrong?
Update
I have set the app transport security and stuff in the info.plist and the printing works correctly if I don't use encryption in php