Wonder Watt website   |   Wonder Watt web app

I’ve just bought HA Green assuming I could control my Growatt inverter but I can’t. I’m on Octopus Agile and Wonderwatt works faultlessly.

13 days later

Depends what you mean with "control". I use WW because I can't get writing to growatt to work. But You can read values. I recommend the integration "Grott" for doing that. Grott sets up a proxy between Your HA and the somewhat unreliable and restricted Growatt API. Thereby You have data, also when growatt server is down.
If You use Node Red, there is a node, "Growatt", which does a decent job reading Growatt values.