Magento 2 – Custom Shipping Method Not Showing on Frontend

I'm trying to create a custom shipping method in Magento 2.1.7. I've followed the tutorial of Mageplaza:

https://www.mageplaza.com/magento-2-create-shipping-method/

The problem is that the shipping method doesn't show in the checkout, after trying multiple things.

I think i'm missing something small, maybe someone knows the answer?

What i've tried:

1. Clearing the caches
2. Enabling the module
3. Changing the module name
4. Applying and changing the shipping method backend configuration
5. Disabling other checkout modules

Code (Mageplaza\Simpleshipping\Model\Carrier):

<?php
namespace Mageplaza\Simpleshipping\Model\Carrier;

use Magento\Quote\Model\Quote\Address\RateRequest;
use Magento\Shipping\Model\Rate\Result;

class Shipping extends \Magento\Shipping\Model\Carrier\AbstractCarrier implements
    \Magento\Shipping\Model\Carrier\CarrierInterface
{
    /**
     * @var string
     */
    protected $_code = 'simpleshipping';

    /**
     * Shipping constructor.
     *
     * @param \Magento\Framework\App\Config\ScopeConfigInterface          $scopeConfig
     * @param \Magento\Quote\Model\Quote\Address\RateResult\ErrorFactory  $rateErrorFactory
     * @param \Psr\Log\LoggerInterface                                    $logger
     * @param \Magento\Shipping\Model\Rate\ResultFactory                  $rateResultFactory
     * @param \Magento\Quote\Model\Quote\Address\RateResult\MethodFactory $rateMethodFactory
     * @param array                                                       $data
     */
    public function __construct(
        \Magento\Framework\App\Config\ScopeConfigInterface $scopeConfig,
        \Magento\Quote\Model\Quote\Address\RateResult\ErrorFactory $rateErrorFactory,
        \Psr\Log\LoggerInterface $logger,
        \Magento\Shipping\Model\Rate\ResultFactory $rateResultFactory,
        \Magento\Quote\Model\Quote\Address\RateResult\MethodFactory $rateMethodFactory,
        array $data = []
    ) {
        $this->_rateResultFactory = $rateResultFactory;
        $this->_rateMethodFactory = $rateMethodFactory;
        parent::__construct($scopeConfig, $rateErrorFactory, $logger, $data);
    }

    /**
     * get allowed methods
     * @return array
     */
    public function getAllowedMethods()
    {
        return [$this->_code => $this->getConfigData('name')];
    }

    /**
     * @param RateRequest $request
     * @return bool|Result
     */
    public function collectRates(RateRequest $request)
    {
        if (!$this->getConfigFlag('enable')) {
            return true;
        }

        /** @var \Magento\Shipping\Model\Rate\Result $result */
        $result = $this->_rateResultFactory->create();

        /** @var \Magento\Quote\Model\Quote\Address\RateResult\Method $method */
        $method = $this->_rateMethodFactory->create();

        $method->setCarrier($this->_code);
        $method->setCarrierTitle($this->getConfigData('title'));

        $method->setMethod($this->_code);
        $method->setMethodTitle($this->getConfigData('name'));

        $amount = $this->getConfigData('price');

        $method->setPrice($amount);
        $method->setCost($amount);

        $result->append($method);

        return $result;
    }
}

Code (config.xml):

<?xml version="1.0"?>
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
        xsi:noNamespaceSchemaLocation="urn:magento:module:Magento_Store:etc/config.xsd">
    <default>
        <carriers>
            <simpleshipping>
                <enable>1</enable>
                <sallowspecific>0</sallowspecific>
                <model>Mageplaza\Simpleshipping\Model\Carrier\Shipping</model>
                <name>Mageplaza Sample Shipping Method</name>
                <price>10.00</price>
                <title>Mageplaza Sample Shipping Method</title>
                <type>I</type>
                <specific_error_msg>This shipping method is not available. To use this shipping method, please contact
                    us.
                </specific_error_msg>
            </simpleshipping>
        </carriers>
    </default>
</config>

Settings: