Think of a firmware file like a physical encyclopedia set sealed in shrink-wrap.
This is the most common cause. You downloaded a 2GB ROM file. It took an hour. Your internet flickered for a split second at the 98% mark, but the browser marked it as "Complete." To you, the file looks fine. To the flashing tool, that micro-second glitch created a "bad sector" in the archive. The "End of Central Directory" signature was corrupted, making the file unreadable. flash failed could not find end of central directory
If fails, try the Raspberry Pi Imager (it works for non-Pi images too) or Rufus . Think of a firmware file like a physical
Understanding why this happens is the first step to fixing it. Usually, it boils down to one of the following: It took an hour
Next time you see it, take a deep breath. Put down the hammer. Your device is safe; you just need a better download.