Last time I tried AFP was a year ago on 9.2,with OSX 10.10 I think, and it was unidirectional, read only... (I don't even remember in what direction sorry).
If that was expected behavior, it for sure wasn't as advertised. Check permissions/ACLs and ownership of share obviously, Mac's firewall, maybe even a port on the router. I have no clue really but I feel your pain, networking can be complex. I wanted NFS for my MAC to Freenas, but I'm kinda new so maybe that's why I couldn't get that working either.
I'd suggest SMB/CIFS, that seems to be working both ways for me with FreeNAS 9.3.