Can login but not sync on raspberry pi and windows/mac clients

I just put a fresh install of Seafile 6.1.1 on my raspberry pi that is running raspbian (debian 8). The only other service running on this pi is SSH. Seriously, no web server, no mail server, no graphic UI, it’s a pretty simple and fresh install.

I’m setting up for syncing inside my home network, so everything is using an internal IP address. Not trying to go through firewall or NAT (yet). I can login to the web interface (seahub) and alter settings, create libraries, upload files, etc.

I’ve tried setting up Mac and Windows clients, but both have the same problem. I can login, and get a list of Libraries on the server, but when I try to sync any of them I get an error: “Cannot connect to server.”

What additional info should I post? Can anybody help me figure this out?