FulGaz can't communicate directly with your Apple watch, but you may be able to link it via a third-party app called HeartCast. To do this, you will need an iPhone to run the HeartCast app and a separate device to run FulGaz (iPad, Apple TV, laptop, etc).
Install HeartCast on your iPhone -> https://www.heartcast.app
Pair your Apple Watch with HeartCast.
This transmits heart rate from your Apple Watch via a Bluetooth channel from your iPhone.
Your Apple Watch HR should appear as "HeartCast-" under the Heart Rate option.