It exists, but unless it comes from a big corp, people don't trust it, and if it does, then it costs a subscription fee. For those who have a leap of faith, paper is much cheaper and more accessible than a 3d printed esp32 computer and a lightning node running somewhere remotely. Fyi, I'm talking about LNbits and their offline payment tool that lets you type a number in sats, generates a QR code, and when you pay it, you get a 6 digit code which the device will also know and if they match, the payment was done. All offline. The payment happened elsewhere, the mini device just hooked you up and used a technology similar to one time passwords to help the merchant verify payment without going to the server.