Canon PIXMA E304 Online Manual page 226

Make sure Enable bidirectional support is selected in the Ports sheet of the
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properties dialog box of the printer driver. (Windows)
If not, select it to enable bidirectional support.
Check the settings of security software's firewall.
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If your security software's firewall is on, a message may appear warning you that Canon software is attempting
to access the network. If this warning message appears, set security software to always allow access.
If you are using any programs that switch between network environments, check their settings. Some programs
use a firewall by default.
If printer is connected to an AirPort Base Station via LAN, make sure you use
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alphanumeric characters for network identifier (SSID). (macOS)
If the problem is not resolved, redo setup.
• For Windows:
Perform setup using the Setup CD-ROM or from the web page.
• For macOS:
Perform setup from the web page.
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