Also on the lcd screen, page down on settings to wifi status and make sure it has a status of connected.
In this thread, a Bluetti admin said (Back in October) it is a software update issue and not to update if you havenât already. Now it is Jan, and still no fix. I could access my new AC300 2 days ago via Bluetooth, and now cannot (since update.) I did not know not to update until I searched for solution 
My general two-cents about a new system is use it. Use it for a few days or a week as you would if the power were to go out. Why? Sometimes issues will pop up and itâs best to work through those issues before itâs an emergency. I am currently working through an issue with the Bluetti tech support where batteries will not balance (AC300 +2 B300 batteries). If I would have just left the system sitting until I needed it, it may have been an issue. This allows me to have a real expectation of the system for my specific application.