I bought a new Nikon D5600 (latest firmware v1.01) and it has BT (Bluetooth) version 4.1.
SnapBridge will only work with the newer BT 4.x technology (see small print on SnapBridge page, on Nikon website). It reads: A device with BT 4.0 or later (i.e. a device that supports BT Smart Ready/Low Energy).
You may have the most current iOS on your device, but if you have BT 2.0 embedded in the device it will NEVER work!
This is probably why so many folks have issues, they are trying to pair with smart devices that are not supported, i.e. they have outdated BT technology in their devices. You can look up BT versions on Apple website for each version of iPhone/IPad, so you can check what is actually embedded in your 'smart' device.
What will NOT work: any smart device (iPhone or iPad) with BT 2.x or 3.x. This version of BT will not work with SnapBridge.
Even an older Ipad 3 with BT version 4.0 did NOT work (at least I could not get it to work).
What DOES work: any smart device with BT 4.x (4.1 and above it seems). My new iPhone 5SE with BT 4.2 works just great with SnapBridge.
Embedded BT technology in a device is not 'upgradable', it does not go from 2.0 to 4.2 with a newest version of iOS !! So even if firmware, and iOS are all current, you are out of luck if you have older devices with embedded BT 2.x, 3.x (and maybe 4.0) technology in it.
Yes, SnapBridge will turn on the cameras BT function (once you have it working and paired). You CANNOT turn BT function on yourself in camera settings (greyed out). SnapBridge can also control your camera, so you can take pics remotely using your phone. SnapBridge uses the WIFI capability of the camera. The camera is acting as a wireless access point, but ONLY Snapbridge can connect/communicate with it, it seems.
I tried other software to connect to the camera, it will not work. The only other thing to control my D5600 is the Camera Control Pro software (full version). Comes at a price (see Nikon site), but it works great with my MacBook Pro laptop.
Windows platform phones do not work with Snapbridge. Only iOS and Android work with Snapbridge, and either one must have BT 4.1 or higher!