The NFC antenna on your phone may be located in different places (Samsung users can find it here). Therefore, it is usually best to slowly slide the ring over the back of the phone, from the center towards the top. When you feel a slight vibration, then a NFC connection has been established.
For a better connection during the process, please remove your mobile phone case if you have one.
Android
To avoid problems during operations, place your ring or wearable on a table and then place the phone with the antenna area against it so that neither the phone nor the ring/wearable moves during the process.
If there are any connectivity problems, try to slightly separate the ring/wearable from the phone by using an object slightly larger than the ring or wearable to hold the phone.
iPhone
The NFC antenna of iPhones is always placed at the rear top side of your phone. Please, see the picture below
