In my head: "Hmm... Interesting. You know how these cards are - the bank will stop everything but actual fraud!"

Out of my mouth: "Hehehe, weird, I swear I've got enough money... Err... Ah... Let me just, um, let me check if the app is acting up. No? Hrmmm... Let me try again..."

"ah, that's a bother. I'll try one of my American Express cards instead, or perhaps my Schwab card."

Gotta start with the mediocre card first, so you can spin the situation in your favor.

Get to spend more time with cute cashier. Win!

This would be my luck.