The MAC Address, sometimes called Physical Address or WiFi Address, is a unique code given to every device. This enables us to see if a device is connected to the WiFi, approve access or diagnose connectivity issues.
iPhone/iPad
Go to: Settings>Wi-Fi>Press on the 
next to the WiFi name.
The MAC address is listed as Wi-Fi address.
From iOS 15 Apple devices have introduced Private Wi-Fi Addressing. If supplying the IT Dept with the MAC address please turn this off and supplying the newly listed address.
Android
Go to: Settings>Internet>Then find the wifi network you have joined>Then go to Privacy>change to 'Use device MAC'
Then Device MAC address is underneath
Windows PC/Laptop
Go to: Settings>Network & Internet>WiFi>Hardware Properties.
The MAC address is labelled as Physical address.
MacBook