I know this is a couple weeks old but wanted to add for your (and others) information that I booked a Mears Connect (the $16 ride shuttle ride) for my son while on our trip 2 weeks ago. Less than 48 hours from when he would be picked up. Plans had changed and he didn't want us to drive him to the airport 8 hours early (who could blame him??). Hopped on my phone, got him booked in just a few minutes and he had zero issues.
(And nobody @me, he's in college. LOL)