If your Zebra ZD410 printer is not printing in line, it could be due to several reasons.

Here are some steps to troubleshoot the issue:

Check the media loading: Ensure that the labels are loaded correctly and facing up. Verify that the roll is properly aligned. 

Inspect for obstructions: Check for any debris or stuck labels in the label path. 

Clean the label sensor: Use a soft, dry cloth to clean the label sensor if necessary. 

Adjust the label guides: Ensure that the label guides are not too tight or too loose. 

Recalibrate the printer: Turn off the printer, hold down the feed button while turning it back on, and release it when the status light starts flashing. 

Update the printer firmware: Ensure that the printer's firmware is up to date.