The printer is showing the message: "Puppy # firmware not found".
Error name: Puppy FW not found
Error code: #17518
The error message includes the name of the puppy board where the firmware was not found. The firmware for all puppies is part of the Original Prusa XL firmware file. The error is triggered when the indicated puppy firmware was not found as part of the firmware file.
Download the firmware and if necessary the bootloader, and transfer it to your USB drive. Make sure to unmount the drive from your operating system before physically removing it.
Insert the USB drive back into the printer and reboot the printer using the reset button directly next to the knob to initiate the flashing procedure. In case the procedure does not start, reboot the printer again by pressing the same reset button, and while the printer is booting up, press once the rotating knob.
The printer will let you know when the flashing is done. When installing the bootloader along with the firmware, it may take several minutes.