User's Guide
Page 67
... missing, or is not inserted completely. ▲ Make sure the rear access panel (HP Officejet Pro K550) or the duplex unit (HP Officejet Pro K550dtn/ K550dtwn) is inserted completely at the back of media into the printer, and press (Resume button). It is jammed in manual duplex mode. The Power light and the Resume light are completely closed completely...
... missing, or is not inserted completely. ▲ Make sure the rear access panel (HP Officejet Pro K550) or the duplex unit (HP Officejet Pro K550dtn/ K550dtwn) is inserted completely at the back of media into the printer, and press (Resume button). It is jammed in manual duplex mode. The Power light and the Resume light are completely closed completely...