macOS Server com.apple.accounts error 10002

Hello all

I've recently tried to set up a Mac Mini (10.12.3) as a server for a few services. I've been using Server 5.2 and have been able to set up some services ok on the local network (file sharing, Time Machine), and have been looking to see if I can set up the server to be available over the internet (for Calendar, Contacts and Mail services), with a view to using it for a small business. However, when I've tried this, and try to connect to the server through the Internet Accounts part of System Preferences, I'm hit with the error "The operation couldn't be completed. (com.apple.accounts error 10002.)"

I've tried searching for what this means and how it can be resolved, but had no luck. I'd be grateful if anyone has any ideas.

Thanks in advance