ive killed every single legionnaire and freed the slaves but now i cant get the ferry to work...any suggestions?

I haven't tried it myself but I saw someone else say if you jump on the barge and look down at your feet you can activate it.

I just activate the transport by clicking on the marker at the end of the dock. Tou won't see anything till you're standing on it. (this was when I was against the legion and had killed everyone (ferryman included).

I was unable to use the raft untill the legion guy gave me an invite from caesar, maybe you can't use it because you haven't had the invite?