Here's the Screenshot in New York, not Miami
That's been active in New York, Chicago, Boston, and other select market... teaching people to be ready, because those people take forever, cars are readily available fairly quick AND traffic conditions can't have anyone waiting for too long in crowded streets.
I can't vouch for that notice to have been implemented in Miami. However, for all UberPool Requests... people typically get charged the $2 and the app states "...because the Driver was on his way." So all one needs to do, is go under help, and the first option is "I was charged a Cancellation Fee." All a pax needs to do is "My driver and I were unable to connect," and they'll credit their account. That easy.