I am toying with the idea of making a large, $40K, tax payment on my Hilton Amex Surpass in order to secure Diamond status for this year and next. I figure the 1.82% fee is justified for the FNC I'll earn plus the value of 120K points. Problem is my credit limit is about $10K. Has anyone had experience requesting a temporary credit limit increase for a large purchase? Any magic words to say when calling in?

Or can I prepay $30K and then make the payment? I think I read somewhere Amex does not allow pre-payments.

I'd like to do this in a single payment in the next few days as this will be a 2024 Q4 Estimated tax payment.