Remote Authentication for support

I have written script for remote Authentication for support in PHP. But it gives

{"result":"failure","cause":"Unauthorized Access"} error.
I think problem in generate Apikey so. I have used MD5 function of php to generate the apikey.
Here is my code : 
$array = array($operation, $email, $loginName, $fullName, $utype, $authkey, $ts); 
 
$apikey = md5(serialize($array)); 

Please guide me what i am doing wrong.

Thanks