After installing the unit in standalone, via my mobile, (which required a TP-LINK ID) I got to a PC and installed the controller, to migrate across and use a singular channel instead of separate 2.4 & 5 Ghz SSID's.

The issue I had at that point is that the controller asks for the exisiting TP-LINK ID, which, I created with my email address as per normal, and without any issue. However when entering the TPLINK ID to make the cloud connection the controller tells me my email address is invalid.

So I had to make a new TP-LINK ID with a different email address. I'd like to point out my email address works perfectly well, and has for many years. Whatever garbage code the controller uses to decide my email address is invalid is clearly at fault here.