Do not use a simple battery charger. Use a (13.8V @ 20A+).
You would be surprised how many "writing buffer" errors are caused by a cheap USB cable. KESS v2 draws significant current during the write phase (much more than during read). checksum error writing buffer kess v2 verified
Always connect a stable battery charger (or a second vehicle via jumper cables) to the car being flashed. Do not use a simple battery charger
means: What Kess sent ≠ What the ECU received. checksum error writing buffer kess v2 verified
The "Checksum error" is the reason for the mismatch.