API Error 10003 - no permissions for users-post API call

Using version 4.2.6, I've set up an API key with user permissions index, get, update, delete and create.

From a php page, I have the code

Code:

<?php
    $url = 'http://example.com/amember/api/users';
    $fields = array(
                '_key' => 'xxxxxxxxxxxxx',
                '_format' => 'xml',
                'login' => strtolower('mark4').time(),
                'pass' => '1111',
                'email' => 'tester3@example.com',
                'name_f' => 'Mark',
                'name_l' => 'tester',
        );
   
   
    $fields_string  = http_build_query($fields);
    //open connection
    $ch = curl_init();
   
    //set the url, number of POST vars, POST data
    curl_setopt($ch,CURLOPT_URL,$url);
    curl_setopt($ch,CURLOPT_POST,count($fields));
    curl_setopt($ch,CURLOPT_POSTFIELDS,$fields_string);
    curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
    //execute post
    $result = curl_exec($ch);
   
    //close connection
    curl_close($ch);
    var_dump($result);
?>

I'm getting "API Error 10003 - no permissions for users-post API call"

I've checked the database and in am_api_key, the entry for this api key is {"users":{"index":1,"get":1,"update":1,"delete":1,"create":1}}

What could the problem be?