I don't have a Z21 system
Ok ... that's a challenge.
First you need to get the WLANMAUS and the ECoS on the same network segment so that they can talk to each other.
The ECoS has a wired network port and the WLANMAUS needs to connect to a WiFi hub, so
- Connect the ECoS to a WiFi hub
- Then connect the WLANMAUS to the WiFi hub.
You should be able to check that both units are connected to the network by logging in to the WiFi hub as 'admin' and checking what devices the hub thinks it can see.
The next challenge is getting the ECoS to recognize the commands the WLANMAUS transmits.
The ECoS will be prepared to listen for commands from ESU's own wireless controller - I have one of these, it runs Android. I am not particularly impressed by it.
If the WLANMAUS can be made to emulate ESU's wireless controller, then you might be in business but I doubt it can do that.
You can find out what the WLANMAUS transmits using 'Wireshark' on a PC to capture traffic on the network but I suspect all you will learn is that the WLANMAUS is working.
What you need is some kind of protocol converter that understands WLANMAUS commands and converts them to ECoS commands. That's the kind of thing a computer control system might do, so maybe check out JMRI to see if it would help?