public function register($args, $payload) {
        $url = $payload['ipnEndpoint'];

        if (empty($url)) {
            return $this->getErrorResponse(self::URL_EMPTY);
        }

        $response = (new EndpointSetter($this->module))->set($url);

        if ((int)$response['ResponseStatus'] !== 200) {
            if (isset($response['Error']['Code'])) {
                if ($response['Error']['Code'] === 'InvalidArgumentsClientError') {
                    return $this->getErrorResponse(self::URL_INVALID, [$response['Error']['Message']]);
                }
            }

            return $this->getErrorResponse(self::INTERNAL_SERVER_ERROR);
        }

        $opts = $this->module->getActingOpts();
        $opts['ipn_endpoint'] = $url;
        $opts['ipn_registered'] = true;
        $this->module->updateActingOpts($opts);

        return 'success';
    }