Samsung Galaxy Watch 4 doesn't work with an iPhone
Amazon.com: Samsung Galaxy Watch Active - 40mm, IP68 Water Resistant, Wireless Charging, SM-R500N International Version (Android/iOS) (Silver) (Renewed) : Electronics
How To Pair Samsung Galaxy Watch To iPhone - YouTube
Amazon.com: Samsung Galaxy Watch (42mm) Smartwatch (Bluetooth) Android/iOS Compatible, SM-R810, International Version (Rose Gold) (Renewed) : Electronics
Galaxy wearables that are compatible with iOS
Galaxy Watch 4 iOS support dropped, Samsung confirms - 9to5Google