add a 2G channel to my Airport Extreme

Thanks for checking on that. This model produces both 2.4 GHz and 5 GHz channels at the same time. So, you cannot "add" 2.4 GHz channels because this is already happening. You can check the Specifications of the AirPort Extreme to confirm below.

I would suggest that you try assigning different names to the 2.4 GHz and 5 GHz signals and then try to connect the camera to the 2.4 GHz network name to see if it can connect that way.......although the camera should connect to your dual band network unless the camera is using older WiFi technology.

If you decide to try this, and you have a Mac, here is how to do this:

Open AirPort Utility on your Mac, locates as follows: Finder > Applications > Utilities > AIrPort Utility

Click on the picture of the AirPort Extreme

Click Edit in the smaller window that appears

Click the Wireless tab at the top of the next window

Click the Wireless Network Options button near the bottom of the window

Enter a check mark in the box next to 5 GHz Network Name

Click Save, then click Update at the lower right of the window and give the AirPort a minute to restart with the new settings

Your 2.4 GHz network is now the normal name of your wireless network. Your 5 GHz network is now the normal name of your network with "5 GHz" added to the name, so it should be easy to identify both networks.

Try and connect the camera to your normal network, which is now the 2.4 GHz network.