Oki MB472dn User Manual page 431

Register the loaded paper in the machine. Proceed to "Registering the Paper Size, Type, or Weight".
Note
Do not load paper of different sizes, types, or weights at the same time.
When adding paper, take the paper in the MP tray out, straighten the edges of both stacks of paper, and then load them.
Do not put anything other than print paper in the MP tray.
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