The key is to get the TV to display the 12-digit code. That must come first, before the 6-digit response code is generated. If it doesn’t, the USB update process has failed before reaching that point, and needs to be retried with a verified working USB and clean firmware file.
A. Verify the USB Drive
Must be FAT32 format.
Recommended size: under 32GB.
No other files on the drive except the update.
Use a known-good USB stick (avoid USB 3.0 if the TV is old — try USB 2.0 if available).
B. Redownload Firmware (Link to Roku's TV Update site)
Corrupt downloads happen.
C. Try another USB port
Some Roku TVs have more than one USB port. If it’s not reading from one, try another.
D. Power-cycle the TV
Remove power completely for 30+ seconds, reinsert USB, and try again.