yii2 bulk action how to update multiple rows in a dropdown menu using checkboxes

I have created a gridview widget. I can select multiple rows using the class CheckboxColumn::class and I can update those rows using the action in my controller. The gridview, button and js look like this:

<?= Html::a(Yii::t('backend', 'Change selected'), ['update-selected'], [
    'class' => 'btn btn-success mb-1',
    'id' => 'updateSelection',
    'data' => [
        'toggle' => 'modal',
        'target' => '#modal'
    ]
]) ?>

<?= GridView::widget([
    'id' => 'prId',
    'dataProvider' => $prSearch->search(Yii::$app->request->queryParams),
    'filterModel' => $prSearch,
    'filterSelector' => 'filter',
    'columns' => [
        [
            'class' => CheckboxColumn::class,
            'name' => 'CheckBoxSelection',
        ],
        [
            'attribute' => 'name',
        ],
        [
            'attribute' => 'visible'
        ]
    ],
]); ?>
<?php
$this->registerJS(<<<JS
var action = '';

$('#updateSelection').on('click', function(event) {
    event.preventDefault();
    submitForm();
});

function submitForm() {
    var url = $('#updateSelection').attr('href');
    var keys = $('#prId').yiiGridView('getSelectedRows');
    console.log(keys);
    $.ajax({
            type: 'POST',
            url: url,
            data: {keylist: keys}
        });
}
JS
    , View::POS_READY);

And here we have the controller:

    public function actionUpdateSelected()
    {
        $pr = new pR();
        if (Yii::$app->request->isPost && Yii::$app->request->post('keylist')) {
            $pr = pR::find()
                ->where(['IN', 'id', Yii::$app->request->post('keylist')])
                ->all();

            foreach ($pR as $pr) {
                $pr->visibility = 0;
                $pr->save();
            }
        }

        return 1
    }

This makes sure all of the selected rows get a visibility of 0 (there are 4) Now I want the user to be able to open a modal with a dropdownlist so he can choose the visibility himself. So i added this to the controller:

$updateForm = new UpdateForm();

        return $this->renderAjax('UpdateModal', [
            'prId' => new pR(),
            'updateForm' => $updateForm,
        ]);

I created the modal and the form:

//modal
<?php $form = ActiveForm::begin(['id' => 'updateSelectedVisibility', 'type' => ActiveForm::TYPE_HORIZONTAL]);?>
    <div class="modal-body">
        <?= $form->field($updateForm, 'id')->hiddenInput()->label(false); ?>
        <?= $form->field($updateForm, 'visibility')->dropDownList([
            0 => 'none',
            1 => 'some',
            2 => 'much'
            3 => 'yes',
        ], ['id' => 'visibility-dropdown']) ?>

    </div>

And i made a form ofcourse:

class updateForm extends Model
{
    /**
     * @var string
     */
    public $id;

    /**
     * @var string
     */
    public $visibility;

    public function rules()
    {
        return [
            [['id', 'visibility'], 'string'],
            [['visibility'], 'required'],
        ];
    }

    public function attributeLabels()
    {
        return [
            'id' => 'Id',
            'visibility' => 'Visibility',
        ];
    }
}

Now I've tried calling the keys array into the modal like this: $keys = Yii::$app->request->post('keylist');

although nothing seems to work. Does anybody know how to do this?