I was having difficulty pairing my Vivosmart with my new iPhone 6. I had paired my Vivosmart with my previous phone (iPhone 4S) without any trouble.
After trying to figure it out on my own for a long time, I eventually tried following the directions in the manual, which didn't work either. I started searching the forums and finally came across something that actually worked.
First off, if it has been paired to a different device (like mine was) make sure you remove it from your old device.
Since all of my apps were automatically transferred to my new iPhone courtesy of iCloud, the Garmin Connect app was already installed and ready for the VivoSmart.
(Note to Garmin Connect users: if you haven't read the manual or just forgot about this important step: remember that you DO NOT connect your VivoSmart through the iOS Settings > Bluetooth area - you connect directly through the Garmin Connect App)
I tried connecting for a while according to the directions and manual at this point. This involves setting the VivoSmart band to pair and instructing the app to search for the device (under Devices in the menu. Obviously this would work.
...Wrong. At this point I removed my device from the app. The app then notified me that the VivoSmart device on my account was not connected to the app and would I like to do that now? Yes, of course - and then same thing. Try to pair from band and try to search for band from app. No luck.
Finally I saw someone mention turning off Bluetooth on the band and then turning it back on. I did this and then followed the previous step of Pair / Search.
It worked.
If you are having trouble pairing your VivoSmart with an iPhone, I hope something in here helps you.