Craft CMS: action input module controller results in 404 - php

Question

I'm making a custom contact form in Craft CMS with a module. The goal is to view all submitted forms in the dashboard and have the possibility to mail after submissions. Submitting the form results in a HTTP 404 – Not Found error.
I made the module, controller and action needed for this. I configured the module in app.php of the config folder and added it to psr-4 in composer.json to autoload it. I know namespacing and routing is a common issue, so I tried a lot of possible combinations.
This is what the folder structure looks like:
modules/
├─ submissions/
├─ Module.php
├─ Controllers/
├─ defaultController.php
The action input of the form looks like this:
{{ actionInput('submissions/default/send-submission') }}
The module looks like this:
<?php
namespace submissions;
use Craft;
class Module extends \yii\base\Module
{
public function init()
{
// Define a custom alias named after the namespace
Craft::setAlias('#submissions', __DIR__);
// Set the controllerNamespace based on whether this is a console or web request
if (Craft::$app->getRequest()->getIsConsoleRequest()) {
$this->controllerNamespace = 'modules\\submissions\\console\\controllers';
} else {
$this->controllerNamespace = 'modules\\submissions\\controllers';
}
parent::init();
}
}
The controller looks like this:
<?php
namespace modules\submissions\controllers;
use Craft;
class defaultController extends Controller
{
protected $allowAnonymous = [
'action' => self::ALLOW_ANONYMOUS_LIVE | self::ALLOW_ANONYMOUS_OFFLINE,
];
public function actionSendSubmission()
{
echo "test";
}
}
Using an actionUrl also results in the same error:
link