It means you have put the wrong size paper in the printer for the print-job, and it is requesting that you replace the paper with standard US letter size paper.
It may also mean that you have the type of paper that you want to print on, but the divider inside of the paper tray is set on a different size -> and then it thinks you have the wrong paper size because the paper doesn’t fit the tray size.
Basically you either want to: put paper in the tray, change the paper in the tray to a different size, or change the position of the tray divider thing.
It means you have put the wrong size paper in the printer for the print-job, and it is requesting that you replace the paper with standard US letter size paper.
It may also mean that you have the type of paper that you want to print on, but the divider inside of the paper tray is set on a different size -> and then it thinks you have the wrong paper size because the paper doesn’t fit the tray size.
Basically you either want to: put paper in the tray, change the paper in the tray to a different size, or change the position of the tray divider thing.