As a Nikon user, with having the functionality of the bluetooth, it definitely eases up life to see those thumbnails even in better higher resolution displays on our mobile screens. The challenges comes when it all stops working.
Over the numerous times, I encountered the problem with the Nikon app that it starts to become too cumbersome to operate when detecting the camera, or it has the camera detected but will fail to enable the WiFi connection.
It was easier to give up on the app, after you have followed the standard instructions of
– Unpairing the camera
– Deleting it off from both the camera and reloading the app
– Restarting your mobile phone/Bluetooth
– Clearing the cache in the app
– Cannot still connect
Is annoying as it will come to the following screen:

And then after waiting for more than few seconds/minutes, it kept coming up with

I tried all those things which are in Help but to no use and I still didn’t want to go to the third party app.
What NIKON support page misses or assumes is that we all are running on the latest version of the camera firmware.
So I ended up going to the Nikon Download center and then downloading the latest firmware.
The app version at the time of writing this is ver 2.6.2 and my camera firmware was running 1.03 while the latest one is 1.10 and it fixed all the issues.
Happy days again and now both work without a need to struggle, installing, re-installing the app.
Check your firmware upgrades before struggling with the app. It is meant to work flawlessly, but it expects you to be running the latest versions of firmware.