If you are a most cyclists, I'd really suggest sticking with Wahoo bike computers. Garmin are nice hardware but just too complicated to have it pair it.
The biggest reason still to get one is because their Radar is just really cool and important if there is lots of traffic.
That being said if you have a Garmin and you can't get it to pair. This is what you have to do. Hat tip to Brad for the basic instructions and YouTube for the rest. No kudos to Garmin at all their site is Useless.
Note that you need this because for things like the 520, it doesn't have a WiFi chip so needs to tether to upload rides. You don't need to do this for the higher end models like the 1080 which can directly upload.
Most of this is folklore and probably only a few steps matter but here you go
- Have as few Bluetooth connections on your phone as possible. I'm a geek so I had over 30, I suspect that Garmin application has a fixed buffer and this was hanging it. Delete the entries like BT_Edge_520 from your Bluetooth profile. There might actually be two profiles. The BT one is apparently the bootstrap.
- Make sure that on the phone you turn WiFi off. Could be a red herring but lost YouTube videos emphasize this. Turn off the Bluetooth too. Note that at least for my iPhone X when you power cycle the phone it will restart WiFi and Bluetooth seemingly randomly by default. So I put it into airplane mode and pray.
- On your Garmin 520 Plus, delete the phone. Disable the phone connection and power cycle.
- Now turn on Bluetooth on the phone and go to the Connect application from Garmin. This thing is just horrible by the way. I can't understand why they have an application that handles Bluetooth.
- Now you choose add device and it will throw a dialog "choose accessory". For me this hangs quite a bit and the Garmin will say fail after 5 minute and you start all over. So say a prayer.
- If it does succeed you will get a blizzard of pairing messages. And the records will sync.
What still remains broken at least for me are
- The phone will stink pairing failed even if it is all working. Don't touch it.
- Their AppStore will still be broken and at least I couldn't download apps like Xert FTP
Anyway. Good luck!!