My fridge freezer stopped working 2 days ago. It is a Bosch active no frost?

Hi
My fridge freezer stopped working 2 days ago. It is a Bosch active no frost KSU45621AU/02.

I have let it de-frost and completely dry out. When I turned it back on the fan at the back of the freezer started up for about 5 seconds then stopped for about 15-20 seconds (the compressor also starts and stops). It started and stopped like this for a few minutes then the temperature lights started flashing and I could hear a clicking noise.

I have removed and bench tested the fan and it runs continuously.

After refitting the fan the freezer temp drops from 24c to 16c before the lights start flashing. After switching it off for 10 minutes then back on again the freezer temp drops to 11c before the lights start flashing and I hear a clicking or knocking noise. The temperature in the fridge does not change significantly.

Any idea what the problem could be? Thanks