This usually happens if you are trying to downgrade to an older version of Android that the bootloader doesn't support. Always try to flash the same or a newer version of the firmware. Conclusion
Click on the tab in Odin and ensure only Auto Reboot and F. Reset Time are checked. Leave all other settings at default. Click the Start button at the bottom of Odin.
You may need to flash the official firmware if you experience: official samsung galaxy a20 sma205f ds stock rom
Use reliable sources like SamMobile , SamFrew , or Frija (a popular tool for downloading direct Samsung servers).
While holding the buttons, connect the phone to your PC using the USB cable. This usually happens if you are trying to
Ensure your phone has OEM Unlocking enabled in developer options before attempting custom modifications, though standard official stock firmware should pass this check automatically.
Flashing a stock ROM wipes your entire device. Back up photos, contacts, and documents to a cloud service or computer. Reset Time are checked
Extract the downloaded file. Inside, you will see five distinct files starting with the following prefixes: BL_... (Bootloader) AP_... (Application/System) CP_... (Modem/Radio) CSC_... (Country/Region/Carrier data - wipes device)