Epson WorkForce Pro WF-M5799 Workgroup Monochrome Multifunction Printer with Replaceable Ink Pack System - Manual (Page 298)

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8. Slide the ink pack tray into the product until it clicks.
Note: If you cannot insert the tray all the way, make sure the top of the ink pack is level with the top
of the tray.
9. When you are finished, close and lock the front cover.