Originally Posted by sburr

Just returned from Miami and code TI1 was accepted without any questions. My reservation required me to check in with an agent at the counter and when he asked if I wanted the optional insurance, I said it's included and he just said "Ok", and there was no mention of an International driver's license. There were also no questions asked when I returned the car on empty.
PHX seems to be the only airport that consistently rejects the code, so I am going to keep trying it elsewhere, with a backup reservation.