Shipping Methods page in admin goes blank after installing

[VkyAtWork]

I installed this module but after installing my shipping method(Store->Configuration->Sales->Shipping Methods) page showing the blank page. If I disable this module page shows all shipping method setting as it should.

Using Magento ver. 2.2.1

and if I check system.log there is an error like this
[2017-11-30 07:23:47] main.CRITICAL: Class Meanbee\MagentoRoyalmail\Model\Config\Source\Methods does not exist [] []

File Methods.php is here on this path Meanbee/Royalmail/Model/Config/Source/Methods.php
And it contains

<?php

namespace Meanbee\MagentoRoyalmail\Model\Config\Source;

use \Magento\Framework\Option\ArrayInterface;
use Meanbee\MagentoRoyalmail\Model\Carrier;

/**
 * Class Methods Backend system config field renderer
 */
class Methods implements ArrayInterface
{

    /**
     * @var Carrier $carrier
     */
    protected $carrier;

    public function __construct(Carrier $carrier)
    {
        $this->carrier = $carrier;
    }

    /**
     * Sets the option array for the small and medium
     * parcel option in admin section of the extension
     *
     * @return array
     */
    public function toOptionArray()
    {
        $methods = $this->carrier->getMethods();

        $options = [];
        foreach ($methods as $value => $label) {
            $options[] = ['value' => $value, 'label' => $label];
        }

        return $options;
    }

    /**
     * Get options in "key-value" format
     *
     * @return array
     */
    public function toArray()
    {
        return array_map(function ($array) {
            return [$array['value'] => $array['label']];
        }, $this->toOptionArray());
    }
}
```
`

[Dhustone]

Royal Mail only support php to v7