They have an algorithm based upon past behavior, and if something is really outside the established “pattern” as far as location and/or amount, it can be flagged and denied, or they’ll call you to verify that it’s really you attempting to make the charge if they can do so.
It can be a definite pain if you inadvertantly get stuck because of it, but it was put into place to help stop credit card fraud. Call the issuer if it happens to you again, verify your identity and they’ll approve it in my experience.
Only happened once in many many years. But I was aware of it after that.
I have gotten “the call” from the credit card company after a large purchase. I have no problem at all with it. As a matter of fact, I like it. Means that there is less chance of fraud.... because the credit card company is liable. Not me. They have access to resources that I don’t have. In this modern “global” world, we need this kind of protection.