https://your-store.com/wc-api/notchpay

/* Customize the Notch Pay checkout button */
.payment_method_notchpay label img {
    max-height: 40px;
}

.payment_box.payment_method_notchpay {
    background-color: #f9f9f9 !important;
}

// Modify payment parameters before creating a payment
add_filter('wc_notchpay_payment_params', function($params, $order) {
    // Add custom metadata
    $params['metadata']['custom_field'] = 'custom_value';

    return $params;
}, 10, 2);

// Do something after a successful payment
add_action('wc_notchpay_payment_complete', function($order, $payment) {
    // Send a custom email
    $mailer = WC()->mailer();
    $mailer->emails['WC_Email_Customer_Processing_Order']->trigger($order->get_id());
}, 10, 2);