Firmware flash failed.

Rooting phone started
Checking custom root image...
Downloading custom root image. Be patient! Do NOT disconnect the phone!
Checking downloaded image.
Present.
Rooting by custom image-based root method...
Flashing firmware...
Switching to download mode.
Waiting for download mode.
Connecting.
SBL Info: Model: SM-G955F, Region: EUR, Provider: OPEN, PDA: G955FXXU4CRL3
Reading PIT from phone.
Flashing boot.img
Firmware flash failed.
Finished at local time: [03.12.19 14:35:10]
WorkID: 54541844