| Error Message | Cause | Solution | |---------------|-------|----------| | Software install failed! | Wrong model firmware | Double-check BND-L21 vs L22 vs L24 | | Incompatible version | Trying to downgrade from custom ROM | Flash stock recovery first | | dload folder not found | SD card not FAT32 | Reformat SD card to FAT32 | | Signature verification failed | Corrupted download | Re-download from mirror, check MD5 hash | | Stuck at 5% | USB cable issue or low battery | Use original cable, charge phone above 50% |