Rest

To use the Rest functionality you need to include the class in the loader or active the API Library. See : full doc

<?
$loader->registerClasses([
    //...
    'Rest' => $config->application->rootDir.'vendor/v-cult/phalcon/src/Tools/Rest.php',
    //...
], true);

Example :

View [sample/test.phtml]

See :
ManagerModel

<form class='action' preventDefault stopPropagation action-data='<?=json_encode([     
        'type' => 'submit',
        'fn' => 'action',
        'class' => 'TestSampleManager',
        'name' => 'save'
    ])?>'>
    <?=\Phalcon\Tag::hiddenField([
        'id'
    ])>
    <?=\Phalcon\Tag::textField('username'))>
    <?=Phalcon\Tag::submitButton([
        'Send'
    ])?>
</form>

TestSampleManager [js]

See :
ActionModel
ActionHelper

TestSampleManager.prototype.save = function(element){
    var that = this;
    this.action.sendForm(this.basePath+"save", new FormData($(element)[0]), complete);

    function complete(result){
        if(!result.success){
            console.error(result.error);
            return false;
        }
        console.log(result.data);
    }
}

SampleController [php]

<?
function testAction(){
    Phalcon\Tag::setDefault('id', time());
}

function saveAction(){
    Rest::init(); // check request validity
    Rest::checkParams(['id', 'username']); // check required params
    try{
      //...
      Rest::renderSuccess();
    } catch(Exception){
      Rest::renderError($e->getMessage()); 
    } 
}