You need to call AMEX before you spend any money at places like adwords or facebook, have them note your account as a "high volume client" and let them know you'll have a lot of repetitive charges from the same merchants. The last time I spoke to an AMEX the rep said their system flags accounts where the same vendor charges the same amount (daily limit) within a certain time frame. From a risk management point of view that is perfectly reasonable but it doesn't work well for us, just call them and make sure they note it on your account.
I warned them before and after...several times. Each time they've said they noted my account. Ha...