Hi,
You need to use the Onecta app to register your Altherma ASHP with your details and give permissions for remote access for your device to appear in the developer portal.
I tried the developer portal and found the same No Products, but the Onecta app has a Service section which allows you to register the devices, link you email / address, Octy as the installer, and allow remote monitoring. After that, you also register for a free 5-year warranty from Daikin.
Did the Octopus install lead explain this? Nope!
Now when I go into the same developer portal, I see a change…:
ONECTA Cloud API
The ONECTA Cloud API enables you to control your Daikin devices.
This video helped, but also didn’t explain the Daikin Onecta registration step to avoid No Products in the dev portal:
I now have Client ID and Client Secret for the API keys.
If this helps, 
this post!