Attempting to add SimpliSafe indoor camera - requires 2.4 GHz networks

> [...] am attempting to add a camera [...]

   "attempting" _how_, exactly?

> [...] Does not work [...]

   Which kind of "Does not work" is this?

> [...] because it requires a 2.4 GHz network. [...]

   What leads you to believe that your WNDR3400v2 lacks "a 2.4 GHz
network"?

   "Does not work" is not a useful problem description.  It does not
say what you did.  It does not say what happened when you did it.  As
usual, showing actual actions (commands) with their actual results
(error messages, LED indicators, ...) can be more helpful than vague
descriptions or interpretations.

   Some gizmos like this, which use some app or other to do the
configuration, require the device with the app to use the 2.4GHz radio,
too.  If you connect the app device to the router using the SSID for the
2.4GHz radio on the WNDR3400v2, then you might have more success
(whatever you're actually doing).

   Visit http://netgear.com/support , put in your model number, and look
for Documentation.  Get the User Manual.  Read.  Look for "Basic
Wireless Settings".

      Note: These settings apply separately to the 2.4 GHz b/g/n and
            5 GHz a/n bands.

> [...] Motorola (Wifi modem) [...]

   What's a "Wifi modem"?  Has it a model number?  (Is it really a
simple "modem", or a gateway (modem+router), or what?)  A simple modem
has nothing to do directly with wireless anything; that's the router's
job.