Wordpress Rest API returns error


Staff member
I'am developing a plugin for wordpress and have trouble with the Rest API.
On my test server it works without a problem. (v4.6.6)
On a different server (v4.4.10) the API returns this error message:

Der Handler f\u00fcr die Route ist ung\u00fcltig","data":{"status":500}}%

The message is in german and means "The handler for the route is invalid." Don't understand why they translate the error messages for an API. Makes no sense for me. :)

The routes on the <a href="http://domain/wp-json" rel="noreferrer">http://domain/wp-json</a> are equal.
Maybe an problem with the different WP versions?

Definition of the route:

function __construct() {
    add_action( 'rest_api_init', function(){
        register_rest_route( 'test_namespace', 'ping', array(
            'methods' =&gt; 'POST',
            'callback' =&gt; array($this, 'ping_test'),
            'permission_callback' =&gt;  array($this, 'myhacks_permission_callback'),
        ) );
    } );

Thanks for help.