Why is the update for firmware not working?
He said that the installation is failed (-4000).... It's the update 01.00.0201.
Can you help me?

It did the same for me but after leaving it on for a few minutes it said it installed.

Hi, there. Sorry for your inconvenience. Could you please check the firmware of your drone and controller to see which version is now? If not,  please refer to the steps below:
1. First, power the aircraft off, let it stand for 10-25 minutes to cool down, and then reconnect DJI Assistant 2 to update.
2. If the update still fails, check whether the firmware is already the latest version through the DJI Fly screen of the remote controller. If it is not the latest version and the update fails, please proceed to the next step.
3. Drop down on the camera view and check whether there is a hardware error regarding the aircraft status. If there is a hardware error, a high probability is that the hardware is malfunctioning and the product needs to be sent back for testing.