Cleaned up the project a bit and included the latest GameCore Unity package in the project itself

Assets/Scenes/SampleScene.unity

@@ -307,7 +307,7 @@ GameObject:
   - component: {fileID: 1498573725}
   - component: {fileID: 1498573724}
   m_Layer: 0
-  m_Name: Magnificent Voice Chat
+  m_Name: Epic Voice Chat Test
   m_TagString: Untagged
   m_Icon: {fileID: 0}
   m_NavMeshLayer: 0

Assets/Scripts/EOSNativeHelper.cs

@@ -37,6 +37,7 @@ public static class EOSNativeHelper
     public static IntPtr AllocateMemory(IntPtr size, IntPtr alignment)
     {
         return Marshal.AllocHGlobal(size);
+        //return HeapAlloc(GetProcessHeap(), 0, size);
     }
 
     [UnmanagedFunctionPointer(Config.LibraryCallingConvention)]
@@ -45,10 +46,16 @@ public static class EOSNativeHelper
     [MonoPInvokeCallback(typeof(ReallocateMemoryFunc))]
     public static IntPtr ReallocateMemory(IntPtr pointer, IntPtr size, IntPtr alignment)
     {
+        // EOS will sometimes request a reallocation for a null pointer, so we need to specifically handle that
         if (pointer == IntPtr.Zero)
             return Marshal.AllocHGlobal(size);
         
         return Marshal.ReAllocHGlobal(pointer, size);
+
+        // if (pointer == IntPtr.Zero)
+        //     return HeapAlloc(GetProcessHeap(), 0, size);
+        //
+        // return HeapReAlloc(GetProcessHeap(), 0, pointer, size);
     }
 
     [UnmanagedFunctionPointer(Config.LibraryCallingConvention)]
@@ -58,5 +65,19 @@ public static class EOSNativeHelper
     public static void ReleaseMemory(IntPtr pointer)
     {
         Marshal.FreeHGlobal(pointer);
+        // HeapFree(GetProcessHeap(), 0, pointer);
     }
+    
+    [DllImport("kernel32", SetLastError = true)]
+    private static extern IntPtr GetProcessHeap();
+    
+    [DllImport("kernel32")]
+    private static extern IntPtr HeapAlloc(IntPtr hHeap, int dwFlags, IntPtr dwBytes);
+
+    [DllImport("kernel32")]
+    private static extern IntPtr HeapReAlloc(IntPtr hHeap, int dwFlags, IntPtr lpMem, IntPtr dwBytes);
+
+    [DllImport("kernel32")]
+    [return: MarshalAs(UnmanagedType.Bool)]
+    private static extern bool HeapFree(IntPtr hHeap, int dwFlags, IntPtr lpMem);
 }

Assets/Scripts/EOSVoiceChat.cs

@@ -63,7 +63,6 @@ public class EOSVoiceChat: IDisposable
 
     /// <summary>
     /// Join an existing chat lobby or create a new one.
-    /// The completion callback is invoked on both success and failure, and can be used to set up the chat lobby's initial parameters.
     /// </summary>
     public void ConnectToChat(string chatLobbyName, uint maxChatPlayers = DefaultMaxChatPlayers)
     {
@@ -330,11 +329,15 @@ public class EOSVoiceChat: IDisposable
         
         // Update the default input device, so we know whether we can actually talk or not
         uint inputDevicesCount = audioInterface.GetAudioInputDevicesCount(new GetAudioInputDevicesCountOptions());
+        Debug.Log($"Found {inputDevicesCount} input device(s)");
+        
         for (uint inputDeviceIndex = 0; inputDeviceIndex < inputDevicesCount; ++inputDeviceIndex)
         {
             var inputDeviceInfo = audioInterface.GetAudioInputDeviceByIndex(
                 new GetAudioInputDeviceByIndexOptions { DeviceInfoIndex = inputDeviceIndex });
             
+            Debug.Log($"Input device {inputDeviceIndex}: ID = {inputDeviceInfo.DeviceId}, Name = {inputDeviceInfo.DeviceName}, Default = {inputDeviceInfo.DefaultDevice}");
+
             if (inputDeviceInfo.DefaultDevice)
             {
                 defaultInputDeviceId = inputDeviceInfo.DeviceId;

Assets/Scripts/MagnificentVoiceChat.cs → Assets/Scripts/EpicVoiceChatTest.cs

@@ -22,10 +22,12 @@ using Unity.GameCore;
 using UnityEngine.GameCore;
 #endif
 
-public class MagnificentVoiceChat : MonoBehaviour
+public class EpicVoiceChatTest : MonoBehaviour
 {
+    // We intend to use predetermined lobby names generated from game-specific match/team/squad information,
+    // so to simulate this we use a static GUID here, as opposed to letting Epic's backend automatically generate a random lobby ID.
+    // This also allows multiple clients to connect to the same lobby without having to communicate the ID among each other.
     private const string DebugLobbyId = "a0f6a51f-6b61-4c95-9ed8-a1d508fe4eb6";
-    private const string DebugBucketId = "foobar";
     
     private readonly StringBuilder status = new StringBuilder("Status:\n");
     
@@ -80,6 +82,7 @@ public class MagnificentVoiceChat : MonoBehaviour
 
         Debug.Log("Xbox Live services initialized.");
 
+        // This delay is just here to give us some time to connect the debugger
         yield return new WaitForSeconds(5f);
 #endif
         
@@ -88,6 +91,7 @@ public class MagnificentVoiceChat : MonoBehaviour
             ProductName = "WW1Test",
             ProductVersion = "1.0.0.0",
 #if UNITY_GAMECORE
+            // EOS SDK on Game Core will not initialize without these memory management function pointers
             AllocateMemoryFunction = Marshal.GetFunctionPointerForDelegate((EOSNativeHelper.AllocateMemoryFunc)EOSNativeHelper.AllocateMemory),
             ReallocateMemoryFunction = Marshal.GetFunctionPointerForDelegate((EOSNativeHelper.ReallocateMemoryFunc)EOSNativeHelper.ReallocateMemory),
             ReleaseMemoryFunction = Marshal.GetFunctionPointerForDelegate((EOSNativeHelper.ReleaseMemoryFunc)EOSNativeHelper.ReleaseMemory),
@@ -368,6 +372,8 @@ public class MagnificentVoiceChat : MonoBehaviour
     
     private void LoadLibrary()
     {
+        // EOS SDK 1.13 uses dynamic library binding in the Editor but does not provide any system functions to actually load dynamic libraries,
+        // so we need to provide those ourselves.
         eosLbraryHandle = EOSNativeHelper.LoadLibrary($@"Assets\Plugins\EpicOnlineServices\Bin\{Config.LibraryName}.dll");
         if (eosLbraryHandle == IntPtr.Zero)
         {
@@ -413,7 +419,12 @@ public class MagnificentVoiceChat : MonoBehaviour
 
     private void OnGUI()
     {
-        GUI.matrix = Matrix4x4.Scale(new Vector3(2, 2, 1));
+        int screenHeight = Screen.currentResolution.height;
+        if (screenHeight == 0)
+            screenHeight = 1080;
+
+        float screenScale = screenHeight / 720f;
+        GUI.matrix = Matrix4x4.Scale(new Vector3(screenScale, screenScale, 1));
         
         GUILayout.Label(status.ToString());
     }

Assets/Scripts/IProductUserMapper.cs

@@ -1,13 +0,0 @@
-using System;
-using Epic.OnlineServices;
-
-/// <summary>
-/// Generic interface for converting between EOS Product Users and platform-specific Player IDs.
-/// The exact rules for mapping from one to the other may differ per platform, e.g. Steam and Epic will use different logic than Xbox and PlayStation.
-/// The methods in this interface are asynchronous, though implementations may choose to pre-cache mappings to speed up the process.
-/// </summary>
-public interface IProductUserMapper
-{
-    void MapProductUserToPlatformId(ProductUserId productUserId, Action<string> platformIdCallback);
-    void MapPlatformIdToProductUser(string platformId, Action<ProductUserId> productUserCallback);
-}

Assets/Scripts/IProductUserMapper.cs.meta

@@ -1,3 +0,0 @@
-fileFormatVersion: 2
-guid: d8a80c90c491474dbe97eba62578254f
-timeCreated: 1625665094

Packages/manifest.json

@@ -1,6 +1,7 @@
 {
   "dependencies": {
     "com.unity.collab-proxy": "1.2.16",
+    "com.unity.gamecore": "file:gamecore/com.unity.gamecore-0.4.6-preview.tgz",
     "com.unity.ide.rider": "1.2.1",
     "com.unity.ide.vscode": "1.2.3",
     "com.unity.test-framework": "1.1.24",

Packages/packages-lock.json

@@ -14,6 +14,12 @@
       "dependencies": {},
       "url": "https://packages.unity.com"
     },
+    "com.unity.gamecore": {
+      "version": "file:gamecore/com.unity.gamecore-0.4.6-preview.tgz",
+      "depth": 0,
+      "source": "local-tarball",
+      "dependencies": {}
+    },
     "com.unity.ide.rider": {
       "version": "1.2.1",
       "depth": 0,