DIAGNOSIS 'Offline' usually means your computer or phone can't talk to the printer over the network. This is almost always a software or connection issue on your device, not the printer itself.
FIX On your computer, go to your system's printer settings and delete the existing 4155e printer queue. Then, re-add it properly. 1) In Windows, go to Settings > Bluetooth & devices > Printers & scanners. Remove the printer. 2) Open the HP Smart app and let it 'discover' the printer on the network and re-install the driver. On a Mac, go to System Settings > Printers & Scanners, delete the printer, and let HP Smart add it back. This fresh install often clears up communication glitches.
IF THAT DIDN'T WORK The printer might have gotten a different IP address from your router. Restart your router, then restart the printer. Wait a few minutes for everything to reconnect. Then open the HP Smart app again—it should find the printer with its new address.
HEADS UP If you have any VPN or advanced firewall software running on your computer, temporarily disable it during printer setup. These security programs can often block the local network discovery that the printer setup needs to work.