Hello, I have a problem with Zebra Z4M Plus

Hi, if is the vertical line, its the print head that need to be replaced,
try to clean the print head and try this to confirm:
turn printer off, press PAUSE button and at the same time, power on, don't release the button, please wait until printer LCD screen come on, then release button. It will print the PAUSE test and after few 3-4 prints, u can turn off and on again otherwise printer not ready to print your labels until u restart it. (pause test stops after 10-15 labels). this pause print just show how the print head is and if come with vertical lines, u will need to replace. other idea is (if u can) turn the bar code different position or on vertical way at label format. Thanks.