To successfully downgrade an HP 8620, the printer generally must not be connected to HP Web Services (HP Connected), as "Web Services" often auto-provision the latest firmware, potentially overwriting the downgrade immediately.
Connect the printer to a PC via a USB cable ; it should be the only USB device connected. hp officejet pro 8620 firmware downgrade
Downgrading the firmware on an is considered a "solid feature" by advanced users because it allows you to regain control over hardware you own, specifically bypassing HP's dynamic security measures that block third-party ink cartridges. To successfully downgrade an HP 8620, the printer
Here’s a detailed write-up on downgrading the firmware of an HP OfficeJet Pro 8620 printer. To successfully downgrade an HP 8620
Displays "Cartridge Problem" or "Missing or Damaged" errors.