I ripped off nostr:npub14mgq3zmg7wc4g5exw6yztlfaypapcvee06quc5msdqujpa6e5d4sztw00t page: https://lnpay.me/
- add point of sale app, product list style, add each "button" as a product
- btcpay > server settings > policies > customization (Display app on website root)