Just an FYI! You might notice that for some devices on iOS 15, Apple masks the end user’s IP address and sends Apple’s IP address to Heap instead.
This is due to iCloud Private Relay, which is part of iOS Privacy updates for iOS 15 (Apple's announcement). iCloud Private Relay is currently available to users with an iCloud+ subscription and devices on iOS 15. You can read the iCloud Private Relay Overview on Apple’s website for more details.
Heap stores the IP address that we are given. Devices that have earlier operating systems (< iOS 15) will still send Heap the user’s IP.
I hope that helps, please comment if you have any questions!