I've not done this with a Mac (yet, though it's on my to-do list), but I have done it with a raspberry pi 2 and I'm sure it's possible on the Mac. I've found that connecting to http://octopi.local doesn't always work (even though it is supposed to in bonjour-enabled systems). For the pi2, I've just looked up the assigned IP address (which will likely be something like 10.0.1.80) and plug that in instead like this: http://10.0.1.80
Check out this link for more assistance: https://github.com/foosel/OctoPrint/wiki/Setup-on-Mac
That seems to get me connected on a more consistent basis.
My problem is that the Raspberry Pi 2b I have doesn't seem to stay visible on the network unless I connect right away after booting the system. I'm not sure if that will be true for the Mac or not. Right or wrongly, I have the thought that this is because the wifi is provided by a dongle, so I've bought a Raspberry Pi 3 and am working on setting that up. I also have an old Mac Mini I was going to use for the same purpose, but people told me on Reddit that was overkill, just get the RPi 2 and OctoPi. It was only $50 for everything. I still plan on using the old Mini for this within the next few months, though.
Please reply and update your progress.
Thanks,
Jason