It is recommended if you plan a purchase that is significantly higher than your normal spending pattern, and particularly if it is out of country, you contact Amex ahead of time and advise them of the amount and location of the purchase. I once had to put an event reception at a Stockholm hotel on my personal card, about $25K in a single shot. Called Amex a week ahead to advise them. They did ask for a bank reference so they could confirm I had an account that could cover that amount.