Asus RT-AC1200GU User Manual page 41

NOTE: PIN code may vary from different providers.
• Username / Password: The username and password will be
provided by the 3G/4G network carrier.
• USB Adapter: Choose your USB 3G / 4G adapter from the
dropdown list. If you are not sure of your USB adapter's
model or the model is not listed in the options, select Auto.
4. Click Apply.
NOTE: The router will reboot for the settings to take effect.
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