Many merchants enable Chivo Wallet for payments but I guess it's rarely used. One time the shopkeeper was literally wiping the dust from the device (and charging it up) to make the tx.
That Tx actually never happened, as I got stuck at QR 1
I will now describe the process, so you can make it to the end (QR3)

QR 1 - USD

Politely explain that you don't have Chivo wallet and you wish to pay in Bitcoin, not ameriDollars

QR 2 - On Chain

Say gracias, however you'd like to pay over the lightning network. Explain that lightning is the same as bitcoin.

QR 3 - Lightning

Scan / Pay / try not to look too smug as you wait for Chivo to realise and acknowledge your payload
If the merchant is upset about having a bitcoin balance instead of USD, you might recommend to use Strike or Blink instead.