Red line indicate

there are many possibility,
1. wrong ribbon installation , make sure there's nothing wrong, if need u may change the ribbon sensor
2. label not detected, change the label sensor
3. Printer need calibrate, turn off the printer, press and hold the feed button then turn on the printer after it flashes a red light , let go the button, it will do a manual calibrate, wait until it finished, it should be back to normal