My iPhone won't pair to my August EP650R headphones
Go to settings -> Bluetooth and make sure the switch is turned on:



Then make sure the headphones are in a range of up to 10 metres and in a state to be paired to the phone. 

If this doesn’t work try:


Turning Bluetooth on and off on both the phone and the device 
Resetting the device and restarting the phone 
Contacting the device manufacturer