HP LaserJet Enterprise M4555 MFP series - Manual (Page 313)

10. Slide the duplexer into the product to install it.
11. Models with a stapler/stacker: Slide the stapler/stacker toward the product until it latches
into place to install it.
12. Models with a stapler/stacker: Reconnect the stapler/stacker connector.
ENWW Paper feeds incorrectly or becomes jammed 293