TKBHOME TZ68e socket not pairing

You may want to want to try paring\excluding closer to the ST hub, same room and under 10ft/3m away with live logging open and your Domoticz hub powered off. Live logging may let you know why the device will not pair.

Assuming you have a UK hub the device “should” just work, but as it is not on the compatibility list there are no guarantees.

http://www.smartthings.com/uk/compatible-products

This would seam to indicate that the ST hub does not see the device it could be a difference between the TKB and Popp firmware as well.