Pay button (any PHP site)

1. Download nexuspay-pay-button.zip and unzip it into a folder on your site, e.g. /pay/.
2. cp config.php.example config.php; fill in API URL, store API key, webhook secret, store name. Keep config.php and orders.sqlite out of version control (ideally outside the web root).
3. Register https://<site>/pay/webhook.php for invoice.paid (Dashboard → Integrations → Pay button).
4. Put a form on any page:

<form method="post" action="/pay/pay.php">
  <input type="hidden" name="order_id" value="1001">
  <input type="hidden" name="amount" value="25.00">
  <button type="submit">Pay with USDT / USDC</button>
</form>

pay.php creates the invoice (idempotent per order + amount) and redirects to the checkout; webhook.php marks the order paid exactly once — put your fulfilment code where the comment says; thanks.php only displays the current state.