DIAGNOSIS Older printers often only support 2.4GHz Wi-Fi and legacy wireless security protocols (WPA/WPA2-TKIP). The AX21's default settings may be incompatible.
FIX Log into the router. Go to Advanced > Wireless > Wireless Settings. Select the 2.4GHz network. Set the 'Version' to 'WPA2-PSK [AES]' or 'WPA/WPA2-PSK [TKIP/AES]'. Do not use 'WPA3-SAE' as most old devices do not support it. Ensure the 'Enable Wireless Router Radio' box is checked. Set the 'Channel' to 1, 6, or 11 and 'Channel Width' to 20 MHz. This is the most compatible configuration. Save. Attempt the printer's Wi-Fi setup again, using the 2.4GHz SSID and password.
IF THAT DIDN'T WORK The printer may use WPS (Wi-Fi Protected Setup). On the router, press the physical WPS button on the back for 2 seconds. The WPS LED will blink. Within 2 minutes, initiate WPS on your printer (usually a button or menu option). This should establish the connection without entering a password.
HEADS UP The AX21's default 'Auto' channel width for 2.4GHz is 20/40 MHz. Some very old devices cannot connect to 40 MHz channels. Forcing 20 MHz ensures compatibility. If WPS is used, it will apply the current 2.4GHz network's security settings. WPA3 is not backwards compatible with most devices manufactured before 2018.