An ANT+ USB Dongle is required to be plugged into your screen device (MacOS/Windows) in order for RGT to be able to connect to your ANT+ compatible device (we do not support ANT connections done through mobile devices that are ANT compatible, or any other ANT mobile attachments).
Please make sure that your Garmin HR sensor is dual ANT/BLE compatible.
If your Garmin HR sensor is only ANT compatible, this is supported only through the use of an ANT USB Dongle plugged into a Windows/MacOS. How to pair via ANT.
If you have a Garmin Tri HRM sensor, this sensor is only ANT+ compatible.