Embeddable checkout (modal)

1. Settings → Store → Sites allowed to embed checkout: add your site origin (this becomes the frame-ancestors policy for /pay/*).
2. On your page:

<script src="https://pay.zenqpay.com/embed.js"></script>
<button data-nexuspay-checkout="https://pay.zenqpay.com/pay/chk_…">Pay with crypto</button>

or NexusPay.open({ checkoutUrl, onStatus, onClose }). The modal posts {source:"nexuspay", type:"nexuspay:status", status, public_id} to your page as the payment progresses. It is a UI convenience only — fulfil from the signed webhook.