app\models\EntityModel::validate PHP Method

    public static function validate($data, $entityType, $entity = false)
    {
        // Use the API request if it exists
        $action = $entity ? 'update' : 'create';
        $requestClass = sprintf('App\\Http\\Requests\\%s%sAPIRequest', ucwords($action), ucwords($entityType));
        if (!class_exists($requestClass)) {
            $requestClass = sprintf('App\\Http\\Requests\\%s%sRequest', ucwords($action), ucwords($entityType));
        }
        $request = new $requestClass();
        $request->setUserResolver(function () {
            return Auth::user();
        });
        $request->setEntity($entity);
        $request->replace($data);
        if (!$request->authorize()) {
            return trans('texts.not_allowed');
        }
        $validator = Validator::make($data, $request->rules());
        if ($validator->fails()) {
            return $validator->messages()->first();
        } else {
            return true;
        }
    }

 public function process()
 {
     $invoice = $this->stateInvoice();
     $invoiceItems = $this->requestInvoiceItems();
     $data = array_merge($this->requestFields(), ['public_id' => $invoice->public_id, 'invoice_items' => array_merge($invoice->invoice_items->toArray(), $invoiceItems)]);
     // map the cost and qty fields to the invoice items
     if (isset($data['cost']) || isset($data['quantity'])) {
         foreach ($data['invoice_items'] as $key => $item) {
             // if it's new or we recently created it
             if (empty($item['public_id']) || in_array($item['public_id'], $this->entities(ENTITY_INVOICE_ITEM))) {
                 $data['invoice_items'][$key]['cost'] = isset($data['cost']) ? $data['cost'] : $item['cost'];
                 $data['invoice_items'][$key]['qty'] = isset($data['quantity']) ? $data['quantity'] : $item['qty'];
             }
         }
     }
     //var_dump($data);
     $valid = EntityModel::validate($data, ENTITY_INVOICE, $invoice);
     if ($valid !== true) {
         throw new Exception($valid);
     }
     $invoice = $this->invoiceRepo->save($data, $invoice);
     $invoiceItems = array_slice($invoice->invoice_items->toArray(), count($invoiceItems) * -1);
     $invoiceItemIds = array_map(function ($item) {
         return $item['public_id'];
     }, $invoiceItems);
     $this->setStateEntities(ENTITY_INVOICE_ITEM, $invoiceItemIds);
     $response = $invoice->load('invoice_items')->present()->skypeBot;
     return $this->createResponse(SKYPE_CARD_RECEIPT, $response);
 }