Connect the printer to the local network via an RJ45 Ethernet cable.

Debris on the printhead or dead pixels/elements on the thermal heating element.

: For developers sending raw ESC/POS commands, enable the HEX option to transmit data exactly as entered.

Close other POS programs. Check Windows Device Manager for the correct COM/USB port number. Incorrect Baud Rate or mismatched Encoding.

Clean the printhead with an isopropyl alcohol swab. Replace the printhead if lines persist.