Originally Posted by
tonei
Did they specifically say you can’t go to a US consulate, or did they just say ‘if you’re overseas you need to go to a US embassy’? Legally there is no distinction between notarial services provided by an embassy vs. a consulate as far as I know.
Consider that the person the OP spoke to at Amex may not even know what a consulate is, and may be reading from reference material that says "When outside the US, only a notary from a US embassy counts."