I have been unable to add the TP15 directly to Eisy using Matter.  When I try I get UD mobile to scan the QR code but it never completes the configuration.  This it with the current beta Matter, UDMobile 1.5.2.  I have also tried using the Matter code with the same results.

The work-around that I have found is to use an Echo Dot (gen 3 or later) to serve as a “thread border router”.  There are several Alexa devices that will do this.  Here is a detailed procedure, sorry to the experts for the step-by-step but I want to make it clear for anyone.

First do not configure the TP15 through the Tapo app.  It will connect fine to the Echo but you can’t get a forwarding code from Alexa.  If you have it installed in Tapo, just delete it and do a reset.

Plug the TP15 into an outlet.  Open the Alexa app – go to Devices, +, Add Device, other, Matter and follow the instructions (note, don’t use the default Alexa install for the TP15.  I expect it installs with another protocol instead of Matter).  Once the device is found you can name it for use with your echo (name doesn’t carry over to UD).  Now in the Alexa app select the TP15 device, settings (gear icon), Other Assistants and Apps, add another (+), copy the set-up code to the clipboard or write it down.

Open UD Mobile, settings (gear icon bottom right), Matter, add (+), paste or enter the code (hyphens not required), submit.  It took a while so be patient.  Accept the synchronize pop-up.  The new device will appear as ZM XXX.1 On-Off Switch.  Tap on it to change the name and save (it won’t show the new name yet).

Open Admin Console – Matter tab, synchronize, new & deleted, yes.  It will appear with the new name.  You can now move it into a folder, add it to scenes & programs as it is now a fully integrated node.

Go back to UD Mobile and synchronize.  The name will update.

This may work with other TP-Link devices but the TP15 is the only one that I have to test with.  I hope this helps someone get through this much easier than it was for me.  I’m sure UD will fix the direct connect before Matter goes to full release.

What you've discovered is that at this point, eisy isn't very good at configuring (commissioning) a new Matter device, but it's becoming better at accepting a shared Matter device from another platform, like Alexa or Google home. That's how we mainly do it at this time. It's still in Alpha testing on the eisy.

49 minutes ago, Guy Lavoie said:

What you've discovered is that at this point, eisy isn't very good at configuring (commissioning) a new Matter device, but it's becoming better at accepting a shared Matter device from another platform, like Alexa or Google home. That's how we mainly do it at this time. It's still in Alpha testing on the eisy.

Thanks Guy. I got that tip from a thread that I found but there was no detail so wanted to make the step-by-step to save new comers the 3-4 hours that it took me to get the sequence and details correct. I'm new to Matter and also Alexa. I have been using isy and Insteon for many years but it was a bit fiddly.

Another thing you mention in your original post: an echo dot isn't a border router. Matter uses IPv6 for it's communications with devices, implemented over traditional ethernet/wifi, and also over Zigbee ("Thread" devices). A border router will bridge the two topologies. Here is a list of the devices that have that functionality:

https://www.matteralpha.com/frequently-asked-questions/complete-list-thread-border-routers