Ah - it's probably the SAVE which I missed by not scrolling down the page. Hitting Connect when first pastng in the key says nothing (so maybe works). Its when exiting and returning to the page that Connect didnt work.
However, I now cant save becasue "Please enter your PV peak capacity in kWh."
I'm being very thick and just cant see a field for PV peak capacity, or a field where I've entered a number not in kWh, and need to ask for help as to whch filed is meant by the save error message.