Fenix5 connect to iPhone

I am trying to debug my app on a colleague's device but am unable to link it to my iPhone. It had Fenix 5X stamped on its rear.

When I try to pair it with Garmin Connect on my iPhone, the watch reports " Download Garmin Connect Mobile for full connected experience"

What does that mean?

 I have Garmin Connect version 4.61.1.3 installed on my iPhone .