You do not have to preload it with money; it's just tied to your credit card like everything else (including the app).
However, at first I had the same experience as you: the Greenlots keyfob never worked, and I had to call in to get the session authorized. Finally one day I took the time to call into Greenlots and troubleshoot it, and it turned out that the numeric code on the keyfob (as I recall, a hexadecimal value like 5A3B7C) had been been mistyped into their data system. There was an a single character typo, so my keyfob was not actually properly associated with the account. If you call in, have them check that, and make them recite the keyfob code s-l-o-w-l-y and with words (alpha bravo charlie delta echo foxtrot) and compare to the code printed on yours.
That should do it. It's a pain because it takes 5 minutes, but you've got a few minutes to kill, right?
