[Lightning-dev] Data piggybacking within the payment_preimage for offline payments in wallets

[ZmnSCPxj]

Good morning Jose,

> > I still have a few doubts however on how the scheme you propose would handle these concerns:
> > a) Price changes: With the piggybacking scheme I propose, the vending machine (or toll both, or whatever) doesn't set the price of the item or service. It only sends the product/service Id to the remote LN Node. This way, prices can be adjusted in real time.
>
> Why would you sell products with widely fluctuating BTC value?
> We sell products with a fixed BTC value!
> And because BTC is deflationary, BTC value of product will never change.
> We can see very readily that BTC price relative to dollar does not change except for dollar inflation rate and there is no such thing as massive bear market.
>

You probably still want your technician to periodically visit vending machines anyway.
This is to check for mechanical damage or attempts to pay via crowbar.
If so, you can regularly have the invoices replenished with more up-to-date prices.

Then your risk is limited to only the period at which your technician visits each vending machine.

Static QR codes are unimportant.
As long as you can generate the invoice at the vending machine, you can show a QR code to pay to.
In addition, the QR code is needed to be stable only up to getting paid and having the product claimed.

Regards,
ZmnSCPxj