I have two chargers and use Tibber for smart charging during night time. If I during day time want to direct charge I push the touch button on the charger for 2 seconds to override the smart charging. This does only work on the master charger. The slave charger does only start charging if the master charger is already charging. The slave charger should be possible to start independent from the state of the master charger.
This is a known behaviour when controlling the chargers through Tibber as Tibber is controlling the whole charging circuit and not each individual charger. This will be changed in the future. Please ask Tibber about the status of that.