How do you issue a challenge to another player in Swift using GameKit?

Question

I've been able to follow some of the limited guides here and on Apple's website to set up a leaderboard and achievements using Game Center / GameKit for Swift (iOS 15). However, I am now stuck in terms of creating player-to-player challenges using Game Center.

I read the post here that made a reference to converting C code to Swift. I've also read through a PDF (not linked since it may be copyrighted) that has a lot of C code. However, I don't know how to convert any of that code to Swift.

I am trying to do the following:

1. Get a list of Friends that the player can send a challenge to
2. Invite a friend from that list to take part in a GKScoreChallenge.
3. Set up a GKScoreChallenge.loadReceivedChallenges() that alerts a player that they have a challenge
4. Resolve the challenge (either cancel it, or adjudicate it in favor of another player once it is completed)

I don't even have a starting place for this. Extensive Googling gets me to Apple's (terrible) documentation pages. There is a reference to a WWDC 2021 video, but I can't find any sample code to follow along and code this in Swift.

Any help would be appreciated. Even a place to start where I can figure this out would be helpful.