Problem with custom payment method

Hi, I tried to make a custom payment method exactly on paypal.
I copied the files from paypal and tried to change the links to the sandbox as in this documentation.

public function getRedirectUrl($params = [])
    {
        return sprintf('http://sandboxsecure.mobilpay.ro',
            $this->getConfigData('sandbox') ? 'sandbox.' : '',
            $params ? '?' . http_build_query($params) : ''
        );
    }

IPN

protected function postBack()
    {
        if (array_key_exists('test_ipn', $this->post) && 1 === (int) $this->post['test_ipn']) {
            $url = 'http://sandboxsecure.mobilpay.ro';
        } else {
            $url = '';
        }

        $request = curl_init();

        curl_setopt_array($request, [
            CURLOPT_URL            => $url,
            CURLOPT_POST           => TRUE,
            CURLOPT_POSTFIELDS     => http_build_query(array('cmd' => '_notify-validate') + $this->post),
            CURLOPT_RETURNTRANSFER => TRUE,
            CURLOPT_HEADER         => FALSE,
        ]);

        $response = curl_exec($request);
        $status = curl_getinfo($request, CURLINFO_HTTP_CODE);

        curl_close($request);

        if ($status == 200 && $response == 'VERIFIED') {
            return true;
        }

        return false;
    }

https://github.com/mobilpay/composer
This is the documentation.
My question is, how exactly could I make this work and be redirected properly?
Can I make this method concrete or should I take a payment method to change it?
What do you think and if you could give me some advice on how I could proceed

Vaishali Agarwal

Dear @DaniD
Hope this guide will help you https://devdocs.bagisto.com/1.x/advanced/create_payment_method.html