Ajax request forbidden - error 403 - strict-origin-when-cross-origin

Hi guys,
I’m using following code in order to get content of table using Ajax-JSON and kartik widget Select2. Unfortunately, I will get error 403 and hint of strict-origin-when-cross-origin. What’s wrong with this code?

Controller:

    public function actionAuswahl($q = null, $id = null) {
        $out = ['results' => ['id' => '', 'text' => '']];
        if (is_null($q)) {
            $query = new \yii\db\Query;
            $query->select('id, plz AS text')
                    ->from('l_plz')
                    ->where(['like', 'plz', $q]);
            $command = $query->createCommand();
            $data = $command->queryAll();
            $out['results'] = array_values($data);
        } elseif ($id > 0) {
            $out['results'] = ['id' => $id, 'text' => \backend\models\LPlz::find($id)->plz];
        }
        Yii::$app->response->format = \yii\web\Response::FORMAT_JSONP;
        return $out;
    }

View:

        <div class="col-md-4">
            <?=
            $form->field($model, 'l_plz_id', ['addon' => [
                    'prepend' => ['content' => 'Plz']]])->widget(\kartik\widgets\Select2::classname(), [
                'data' => \yii\helpers\ArrayHelper::map(\backend\models\LPlz::find()->orderBy('id')->asArray()->all(), 'id', 'plz'),
                'options' => [
                    'placeholder' => 'PLZ selektieren',
                    'id' => 'zip_code'
                ],
                'pluginOptions' => [
                    'allowClear' => true,
                    'minimumInputLength' => 3,
                    'language' => [
                        'errorLoading' => new JsExpression("function () { return 'Waiting for results...'; }"),
                    ],
                    'ajax' => [
                        'url' => Url::to(['/pa-patient/auswahl']),
                        'dataType' => 'json',
                        'data' => new JsExpression('function(params) { return {q:params.term}; }'),
                    ],
                    'escapeMarkup' => new JsExpression('function (markup) { return markup; }'),
                    'templateResult' => new JsExpression('function(data) { console.log(data.ort); return data.ort; }'),
                    'templateSelection' => new JsExpression('function (data) { return data.ort; }'),
                ],
            ]);
            ?>
        </div>