Error when trying to accept a native js popup with Codeception and Yii2

I'm trying to close a confirm js popup generated by Yii2 for confirm the deletion of a record, in this case a user, with Codeception and his.

Above is the error:

[WebDriverException] JSON decoding of remote response failed. Error code: 4 The response: 'Invalid Command Method - Request => {"headers":{"Accept":"application/json","Content-Length":"0","Content-Type":"application/json;charset=UTF-8","Host":"127.0.0.1:4444"},"httpVersion":"1.1","method":"GET","url":"/alert_text","urlParsed":{"anchor":"","query":"","file":"alert_text","directory":"/","path":"/alert_text","relative":"/alert_text","port":"","host":"","password":"","user":"","userInfo":"","authority":"","protocol":"","source":"/alert_text","queryKey":{},"chunks":["alert_text"]},"urlOriginal":"/session/cac855f0-e7f8-11e4-ae75-8baa74cf41b1/alert_text"}'

Above is my code:

<?php 
$username = 'foobar';
$email = 'foo@bar.com';

$I = new AcceptanceTester($scenario);
$I->wantTo('Check that users can update their passwords');

$I->haveInDatabase('user', array('username' => $username, 'email' => $email));
$id = $I->grabFromDatabase('user', 'id', array('username' => $username, 'email' => $email));

$I->amOnPage("/backend/web/index.php/user/$id");
$I->see('Borrar');
$I->click('Borrar');

$I->wait(3);
## This line throws the error
$I->seeInPopup('eliminar este usuario');
## Trying to change to the popup. This doesn't throw any error
$I->executeInSelenium(function (Webdriver $webdriver) {
   $handles=$webdriver->getWindowHandles();
   $last_window = end($handles);
   $webdriver->switchTo()->window($last_window);
});
$I->pressKey('body', \WebDriverKeys::ENTER);
## This throwed the error before
$I->acceptPopup();
$I->wait(1);

$I->seeInCurrentUrl('user/list');
$I->dontSeeInDatabase('user', array('username' => $username, 'email' => $email));