Hi,
I have a very similar problem with my SolarFlow 2400 AC. The device cannot be paired with the app via Bluetooth or WiFi despite multiple attempts including a factory reset.
I have been in contact with Zendure support and they have acknowledged that the unit is likely defective due to a hardware fault in the internal communication module. However, despite opening two support tickets, they have still not provided any solution or replacement.
It is frustrating to see that this seems to be a recurring issue with the 2400 AC. If you find a solution, please let me know. I will do the same.
Good luck!