Customs House parking with Spot Hero?

I’m new to Spot Hero and using it for the first time tonight. I reserved a spot in the Customs House lot on 8th. Has anyone ever reserved a spot there? How does it work? Looks like there is a gate, but it’s not a lot with an attendant. Guess I’m curious how the gate opens, and how an unattended lot can insure a space will be available. Any insight to ease my never-done-this-before anxiety is greatly appreciated.