PHP中的Hmac-sha1

I've spent several hours reading through many posts already trying to get this to work and am still having issues with it. I'm trying to use the protectedpdf api which requires a three step process to login and receive an auth token, involving the hmac_sha1 hashing algorithm.

I'm making use of the hmac_hash() function in php so the code is simply:

$accessKey = "test";
$dataString = strtolower((string)$clientNonce.(string)$serverNonce.$accesskey);
$clientHash = strtoupper(hash_hmac('sha1', $dataString, $accessKey));

Where ClientNonce and ServerNonce are uuids like 30df805c-27d6-4df1-b482-48b685cc8f54

For a sample set of Client and Server Nonces, the built-in php function returns: C39B753E50DB06DF3DE8E41C682FA8151B49ECBD and i get an authentication error in response to the login attempt.

Using the free formatter hmac generator online tool the same input yields: 7f48c3018c0e53a0b64a60bb7809c7a20a80c9a2

I would greatly appreciate any help - thanks!!!