First - MAC stands for Media Access Control - it's an address built into the device when it's made. (And, in the case of an Android phone, there are two - one for the Wifi connection and one for the mobile data connection.) The reference in this app is to a computer running macOS, which would be a Mac or iMac. Big difference between MAC and Mac. (Case counts in computers.)
As for being near the Mac computer, you can forward port 22222 to the Mac in your router
, then put your external IP address into the weMessage app, or you can not
do that and put the internal
IP address of your Mac computer into the weMessage app. In the first case, you can be anywhere you can get internet access (even overseas). In the second case, you have to be close to the Mac computer - definitely in the same house, probably within one or two rooms at most. (The full instructions are at the weMessage site Installation Guide
, starting at Installing weServer
.) (Note that if you don't have a device running macOS, the app is useless to you. No device not made by Apple can send or receive iMessages. Apple owns the protocol and won't allow anyone else to use it.)
The only problem with using your external IP address is that it can change from time to time. The normal way of handling this is by using a Dynamic DNS service (they're free), that keeps track of your external IP address, and you can set the app to the named address you get (something like me.dynamicdns.com), but there's no mention of whether the app will accept a named address for the weServer, so I've sent the developer an email asking whether it can be done and, if not, whether it can be added. Keep watch here in Android Apps if you want to use weMessage that way. I'll post the response, if any, with weMessage in the topic. (It could be days, or even weeks, until I get a response.) I don't have Apple anything, so I can't check that part out myself.
You should, according to their recommendations, keep your Mac on at all times, and don't put it to sleep. You may
if the Mac is off, start transferring messages to your Note 8 once you turn the Mac on, but they don't guarantee it.