It’s his credit card company’s security software. Sometimes when I’m traveling my company will randomly deny a charge because it doesn’t fit my usual pattern. I have to call customer service and verify the charge to get it turned back on. It can be really annoying.
Banks are doing this a lot these days, mostly because they're on the hook for fraudulent activity. I travel frequently as well and I always call my bank to let them know where I'm going.
Happened to me recently when we were purchasing some entertainment in Long Beach for Catalina Island....declined. I just pulled out another card and it went through.