Just had email from them about it (currently on Octopus GO).
Looks like you need to upgrade to latest firmware (which I haven't done yet)
I have recently switched to IO and I have not updated any software in the car since I purchased it new in Feb 2021. I did have some issues getting the test charge to work - details below. Of course it may just be luck that the fifth try worked but it least it shows a way the can work.
Details of attempts to do test charge
The login to Kia worked as expected and I got to "Test connection". I had the screen "Testing your connection now... not long to go" for some minutes and it reported that it had failed.
I had logged myself out of Kia Connect before I tried this as other people on the forums had suggested this may be helpful.
I then l logged back in and confirmed that I could indeed start and stop charging manually via Kia Connect although the car was scheduled to charge from 00:30 to 4:30. I could see the green light on the charger come on, the charge indicator on the car and the power go up on the home energy display so I know it worked.
This confirms to me that intelligent octopus ought to be able to do the same thing.....
Second test charge also failed
Logged out of Kia Connect and tried again
Third test charge attempt started at 23:19 ended at 23.26 failed again
Removed scheduled charging from the car - now it is charging when IO tries to do test.
Fourth test charge attempt started at 23:30 (Charging on expensive electricity) ended at 23:37 failed again
Logged back into Kia Connect and manually stopped charging - so now schedule is not set on car, car is definitely able to receive external start and stop commands
Fifth test charge attempt started at 23:39
This time finally something happened as I saw the charge start and then stop via my home energy monitor
HOORAY It finally worked