Select the menus on the control panel as described below.
Settings > Guide Functions
Displays a warning if the paper settings (print settings) for the print job do not match the printer's paper settings made when you loaded the paper. This setting prevents misprinting. When Paper Configuration is disabled in the following menu, the paper setting screen is not displayed. In this situation, you cannot print from an iPhone, iPad, or iPod touch using AirPrint.
Settings > Printer Settings > Paper Source Setting