[Bug] Dynamic Links iOS error: "Deep Link does not contain valid required params"

[REQUIRED] Please fill in the following fields:

• Unity editor version: 2020.3.22f1
• Firebase Unity SDK version: 8.7.0
• Source you installed the SDK: Unity Package Manager
• Problematic Firebase Component: Dynamic Links
• Other Firebase Components in use: None
• Additional SDKs you are using: N / A
• Platform you are using the Unity editor on: Windows, Linux, and Mac (I have CI using all 3 daily)
• Platform you are targeting: iOS, Android, and Desktop
• Scripting Runtime: IL2CPP

[REQUIRED] Please describe the issue here:

I’m using Firebase Dynamic Links for Unity, and I’ve got it working well with Android. I’ve even got a solution for Desktop, where the fallback link takes users to a webpage where I can provide instructions to the user for how to get their link content on Desktop.

On iOS, however, I always get errors showing up in the Xcode logs whenever I test dynamic links on iOS, saying “Deep Link does not contain valid required params”. I also don’t get any log that should immediately happen whenever a dynamic link is received. I’ll put the error and code below.

Steps to reproduce:

Have you been able to reproduce this issue with just the Firebase Unity quickstarts (this GitHub project)? N / A What’s the issue repro rate? 100%

This is the full error that appears when an iOS user clicks on https://cgs.link/zu_tiles_hime:

[Firebase/Analytics][I-ACS023001] Deep Link does not contain valid required params. URL params: {
    "_cpb" = 1;
    "_cpt" = cpit;
    "_fpb" = "CIAIEIAGGgVlbi11cw==";
    "_iipp" = 1;
    "_iumchkactval" = 1;
    "_iumenbl" = 1;
    "_osl" = "https://cgs.link/zu_tiles_hime?_iipp=1";
    "_plt" = 260;
    "_uit" = 1064;
    apn = "com.finoldigital.cardgamesim";
    cid = 8062347334713659136;
    ibi = "com.finoldigital.CardGameSim";
    isi = 1392877362;
    link = "https://www.cardgamesimulator.com/link%%3Furl%%3Dhttps://www.cardgamesimulator.com/games/zu_tiles_hime/zu_tiles_hime.json";
    sd = "Play Zu Tile: Hime on CGS!";
    si = "https://www.cardgamesimulator.com/games/zu_tiles_hime/Banner.png";
    st = "Card Game Simulator - Zu Tiles: Hime";
}

Relevant Code:

        private void Start()
        {
            FirebaseApp.CheckAndFixDependenciesAsync().ContinueWithOnMainThread(task =>
            {
                var dependencyStatus = task.Result;
                if (dependencyStatus != DependencyStatus.Available)
                {
                    Debug.LogError("Could not resolve all Firebase dependencies: " + dependencyStatus);
                    return;
                }
                DynamicLinks.DynamicLinkReceived += OnDynamicLinkReceived;
            });
        }
        private void OnDynamicLinkReceived(object sender, EventArgs args)
        {
            Debug.Log("Dynamic Link Received!");
...

EDIT:

Additional Context:

I’ve actually been able to get it somewhat working on iOS by replacing DynamicLinks.DynamicLinkReceived += OnDynamicLinkReceived with Application.deepLinkActivated += OnDeepLinkActivated, but then that only works with long links since only the long link would provide the requisite information to Application.absoluteUrl. I really want to be able to keep shorts links like https://cgs.link/zu_tiles_hime without having to give long links to users. Luckily, if an iOS user types this short link into a web browser, they get sent to a preview page, and that preview page has a button that uses the long link, which works. Ideally, though, that iOS user should be able to just click on the short link without having to type it into a web browser. I’d really appreciate any help with figuring this out!