Why?
The reason for this problem is that the old carbon paper is reused.
How to solve?
Reload the carbon roll, follow the steps below to solve this problem:
Power off the printer and the power button is located on the left side of the printer.
Open the printer cover, press the cover-open buttons located on both sides of the printer to lift and open the cover.
Open carbon holder, press the carbon-open button (blue) to open the carbon holder.
Reload the carbon roll. Push the blue gear on the left and push until you see the new carbon paper.
Close the carbon holder and printer cover, press it till you heard 'DA' sound.
Last, power on the printer and you are all set!
As simple as that 😉