Summary
American Express is one of the strictest issuers when it comes to spending behavior. They are sensitive to sudden spikes in utilization and same-day velocity, especially on new accounts. Large single charges that approach the limit are likely to be declined without prior notification. To avoid interruptions, Amex prefers clients to ramp gradually, demonstrate steady usage patterns, and call ahead for unusually high purchases.
Best Practices
Keep utilization under ~90% of your limit.
Start with smaller test purchases, then scale.
Notify Amex in advance if you plan a large transaction.