OK heres the answer - its not intuitive at alkl and drove me crazy!!
There is a pairing option on the watch - if you dont activate it and use the other links etc on the app and even the phone without bringing up pairing IT WONT PAIR. It must pair to sync so focus on that!
Go on the wrist watch HR, press the button, slide to Bluetooth, switch it on and THEN look for pairing and activate it on the phone
Seriously this will sort it - whoever wrote the program for this needs shooting - its not intuitive at all