Does the unit need to be on to charge with solar panels?
You did not define what unit, but all Bluetti units need to be on to accept solar power and charge the battery or convert to AC power.
Further to that, as far as I know (I have 3 different models) when a power station is connected to an AC or DC charging source that is powered up, the power station should “Auto” turn itself on. You should not need to physically turn it on. If that is happening, it is likely one of two causes; 1. The source power is not at a level or condition suitable for charging, or, 2. The power station is possibly faulty. 