Hello, try to use this way it will work:

$username='Access ID';
$password='Secret Key';
$URL='https://lsapi.seomoz.com/v2/url_metrics';
$payload = json_encode(array("targets" => ["moz.com"]));

$ch = curl_init();
curl_setopt($ch, CURLOPT_URL,$URL);
curl_setopt($ch, CURLOPT_TIMEOUT, 30); //timeout after 30 seconds
curl_setopt($ch, CURLOPT_RETURNTRANSFER,1);
curl_setopt($ch, CURLOPT_HTTPAUTH, CURLAUTH_ANY);
curl_setopt($ch, CURLOPT_USERPWD, "$username:$password");
curl_setopt($ch, CURLOPT_POSTFIELDS, $payload);
curl_setopt($ch, CURLOPT_HTTPHEADER, array('Content-Type:application/json'));
$result=curl_exec ($ch);
$status_code = curl_getinfo($ch, CURLINFO_HTTP_CODE);   //get status code
curl_close ($ch);


print_r(json_decode($result, true));