Compatibility of Android Genie

> My code on the bottom of my wifi/modem [...]

> [...] my admin code [...]

    What does Netgear call this "My code" and this "my admin code"?

   Visit http://netgear.com/support , put in your model number, and look
for Documentation.  Get the User Manual (at least).  Read.  Look for
"Types of logins".  Further reading might not hurt, either.

> [...] the Android Genie app [...]

   I'd use a web browser, rather than any Netegar-supplied app.

> Model: R7500v2|Nighthawk X4 AC2350 Smart WiFi

   Is that accurate? "R7500v2" is a model number; "AC2350" is not.

> With it the AC2350 connected I cannot access any form of controls
> [...]

   "cannot" 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.

> [...] my cell phone Nighhawk app does recognize the AC2350 is present
> and running, but will not allow me to sign in for adjustments. None of
> my passcodes work to sign it on that app, [...]

   Regarding "will not allow me", see "not a useful problem description
[...]", above.

   I'd use a web browser, rather than any Netegar-supplied app.

   The non-psychics in your audience might not know which of your "my
passcodes" you tried, or whether any of them might be appropriate.  (See
"Types of logins", above.)

   Setting both the C3700 and the R7500v2 to use the same "admin"
password might reduce confusion.

> [...] I am thinking maybe since my IP address is not the same as where
> the AC2350 was first registered and connected, nothing will allow me to
> sign in to anything.

   When configured as a wireless access point, the R7500v2 would get a
new/different LAN IP address.  I don't know if any of the Netgear apps
can deal with that situation.  I'd use a web browser, rather than any
Netegar-supplied app.

   By default ("Get dynamically from existing router"), the
R7500v2-as-WAP will get that new address from (the DHCP server in) your
main router (C3700).  Hence, an "Attached Devices" report from your main
router should tell you what the new address of your R7500v2-as-WAP is.
Pointing your web browser at that IP address should get you to the
R7500v2-as-WAP management web site, whether or not any Netegar-supplied
app can deal with it.  And the usual LAN IP address of the main router
("192.168.0.1"?) should (still) get you to its management web site.

   "routerlogin" names might still work, but the results might depend on
where the computer/device is connected.  Using the IP address(es) would
be more reliable.

> This is almost certainly because you have a modem/router in front of
> the second router.

   That is largely drivel (and, as a mantra, unhelpful).  At least one
of us noticed that you agreed to "doing this as an access point" a while
ago, which would eliminate any double-NAT problems.