I bought DJI Mini 2 SE a month ago (not second hand). 2. During my flight, I detected a problem with the horizon line. You can watch it in the video below.
https://www.youtube.com/watch?v=sw3eK_qeZ_Y  
To solve this problem, I tried to solve the problem by reinstalling the firmware with "DJI Assistant 2 (Consumer Drones Series)". However, I could no longer fly the Aircraft with the DJI Fly application. I'm getting the following errors. I also logged out of my account. When I tried to activate the Aircraft again, I failed. I noticed that the serial number of the aircraft is no longer visible. I think "DJI Assistant 2 (Consumer Drones Series)" installed incompatible firmware or something else. Currently active firmware is 01.07.0200. Can you help with this?

Hi there. Sorry about the trouble. If restarting the app doesn't solve the issue, please send me the following information through DM:
1. SN of the drone and remote controller
2. Mobile phone system and version number (Android/iOS)
3. App version
4. App log
To get the app log please follow the steps below:
1. Connect the Android device to a computer using a USB cable. The “USB” connection mode will appear on the mobile phone. Select “File Transfer”.
2. Double click “My Computer”:
3. Find the corresponding Android device and double-click it.
4. Double-click “Internal Storage”.
5. Find the “DJI” file folder and click it.
6. Select the corresponding file folder and double-click it according to the DJI product used.
We will provide your feedback to the DJI engineers for further troubleshooting of the issue.