Attempting to install a 64-bit ROM with a 32-bit recovery (or vice versa), or using an outdated version of TWRP for a newer Android version (e.g., using TWRP 3.1 for Android 9/10), often triggers this failure. Encryption Issues:
If you tried steps 1–8, post in your device's XDA Forum or Telegram group with: error 255 twrp flashing rom