$ composer require czende/gopay-plugin

Add plugin dependencies to your AppKernel.php file:

public function registerBundles()
{
    return array_merge(parent::registerBundles(), [
        ...
        
        new \Czende\GoPayPlugin\GoPayPlugin(),
    ]);
}

Add your test credentials in Sylius admin as new payment method. Complete couple of orders with different states and send email to GoPay authorities. After the review you will get production credentials, so just change it in Sylius admin and you are ready to go.