DIAGNOSIS Yeah, this one's common. The printer's wireless setup is finicky, especially with dual-band routers (2.4GHz and 5GHz). The DeskJet 2855e only connects to the 2.4GHz band.
FIX First, make sure you're connecting to the 2.4GHz network. Its name might be something like "YourNetwork_2G". During setup with the HP Smart app, when it asks for the password, there's a hidden step. If it fails, go back and on the network selection screen, tap the three dots or 'Advanced' and choose "Set up a new network". Re-enter the 2.4GHz name and password there—this often bypasses a glitch in the direct selection method.
IF THAT DIDN'T WORK The printer's wireless module might need a reset. Turn the printer on, then press and hold the Wireless and Cancel buttons together for about 5 seconds until the lights blink. This resets the network settings. You'll have to start the setup process in the HP Smart app from scratch.
HEADS UP If your router broadcasts a single name for both bands (band steering), the printer will often fail. You'll need to log into your router and temporarily disable the 5GHz band or split the networks into two separate names just for the setup.