DIAGNOSIS This is almost always a step in the wireless setup that got skipped. The printer needs to join your home network first, before your devices can talk to it.
FIX Let's do it from the printer's panel. 1) Press the 'Wi-Fi' button on the printer. 2) Use the arrow keys to select 'Wireless LAN setup' and press OK. 3) Let it search, then select your home network name (SSID) from the list. 4) Enter your Wi-Fi password using the keypad. Once it connects, the Wi-Fi light should be solid. Now try adding the printer on your computer or phone again.
IF THAT DIDN'T WORK If the printer can't see your network, you might be too far from the router, or there could be interference. Try moving the printer closer temporarily for setup. Also, ensure you're not using a 5GHz-only network; this printer needs a 2.4GHz signal.
HEADS UP The initial setup often works more reliably using the WPS button on your router. If your router has one, press the Wi-Fi button on the printer, select 'Other methods', then 'WPS (Push Button)', and press the WPS button on your router within 2 minutes.