All our Coinos users get a static LNURL like this: https://coinos.io/p/bob

If you visit that URL when there's an active invoice for "bob" created in the last 5 minutes, it will have the minSendable and maxSendable amounts set to the amount of the invoice, otherwise the sender gets to choose how much to pay.

The NFC tag has a URL that looks like this: https://coinos.io/ln/lnurl1dp68gurn8ghj7cm0d9hx7uewd9hj7up0vfhkysuzmtk

The lnurl at the end there is the encoded version of the static LNURL from above. By passing it at the end of that /ln path we're telling Coinos that we want to pay it.

If you're logged into Coinos with auto-pay turned on for that recipient, it'll just get paid immediately

If you're logged into Coinos but without auto-pay, you'll see a confirmation screen and a "send" button

If you're not logged into Coinos at all, you'll see a QR code and a button to "open wallet" which should launch your Lightning wallet app of choice.

So users don't need to have anything special on their phone to tap the NFC tag. They just have to have NFC enable (which is always the case in iOS) and the link should open in their web browser.