Failed to authenticate user on Cloud.Objects.update

Hi everyone, I'm developing a project using Titanium with Appcelerator. At the moment, the thing I'm trying to do is the following: + Inside my custom objects, in a table called "menu", I have a list of items + Those items have an attribute called "available" (boolean) with true as default value + I want to press a button on my app interface to set the attribute value of a specific item as false When I press that button I get this error on Titanium console:

[ERROR] : 400: Failed to authenticate user [INFO] : ALERT: (KrollRuntimeThread) [17303,19424] Error: [INFO] : ALERT: Failed to authenticate user

Here is the code:

button.addEventListener('click',function(e) {
 
       Cloud.Objects.update({
            classname: 'menu',
            id: p.id,
            fields: {
                available: false,
            }
            }, function (e) {
                if (e.success) {
                    var car = e.cars[0];
                    alert('Taken');
            } else {
                alert('Error:\n' +
                    ((e.error && e.message) || JSON.stringify(e)));
            }
       });
 
       Titanium.API.info("You clicked the button");
    });

Do you have any suggestions? Why can I query for results but I can't update? Maybe a permission problem? How can I fix it? The "p.id" works correctly, it gets the correct item's id.