Why not setup a time period on the inverter that covers the period / opt to force charge, that way during this period, the grid can be used to charge the car and battery, surely this would be simpler than implementing a 3rd party system, that could complicate matters further, especially with intelligent tariffs! (Eon Next Drive gives 7hrs @7.5p.
Is your Zappi wired grid side and the CT clamp wired grid side, which if so the Fogstar battery shouldn’t be able to see Zappi charger?
However, if you have the urge to use Home Assistant, with an intelligent tariff –
I’ll assume you know HA basics😂
You could use an add on like “Predbat”, available on Github which It integrates with the inverter, octopus’s API and as a solar forecast, which is able to control what the battery is doing. Also, it makes sure your Fogstar battery doesn’t discharge into the car, during off peak rates and can charge the battery whenever electricity is cheap, including in any extra cheap slots you get.
Another possible option, is to use MQTT board with “HACS” (Github) or ESS & MultiPlus Control vwith MQTT on HA. There are other options using MQTT,
Example using Givenergy
Is your Zappi wired grid side and the CT clamp wired grid side, which if so the Fogstar battery shouldn’t be able to see Zappi charger