First verify that you have correctly placed the thermal paper in the terminal, checking that the outside of the paper is towards the printer head.
To distinguish the outside, lightly carve it with a metal object to see if it leaves a dark trace.
Then, follow these steps depending on your card terminal model:
A920 Pro, A920, A910, A80
From the Menu you select System, Settings, Printing, and Printing Quality
Choose High Quality- Slow Speed and test receipt printing
If the quality of the test print has not improved, you should contact our Customer Support Team for further assistance.
S900, S800, Ciontek CS50C, Ciontek CS30PRO
If the quality of the print did not improve after the correct placement of the paper, you should contact our Customer Support Team for further assistance.