Host sets one string key. Clients read it on change.

Host: broadcast package list

// host only
void BroadcastLoadedPackages(INetworkingService svc, IEnumerable<string> packages)
{
    const string KEY = "PEAK_PACKAGES_V1";
    svc.RegisterLobbyDataKey(KEY); // safe to call on all peers

    // serialize: escape '|' then join and compress+base64 option
    string joined = string.Join("|", packages.Select(p => p.Replace("|","||")));
    string payload = Convert.ToBase64String(System.Text.Encoding.UTF8.GetBytes(joined));
    svc.SetLobbyData(KEY, payload); // host-only action
}

Client: receive update

void SubscribeToPackageUpdates(INetworkingService svc)
{
    const string KEY = "PEAK_PACKAGES_V1";
    svc.RegisterLobbyDataKey(KEY); // register the key used by host
    svc.LobbyDataChanged += keys =>
    {
        if (!keys.Contains(KEY)) return;
        var payload = svc.GetLobbyData<string>(KEY);
        if (string.IsNullOrEmpty(payload)) return;
        var joined = System.Text.Encoding.UTF8.GetString(Convert.FromBase64String(payload));
        var packages = joined.Length == 0 ? Array.Empty<string>() :
                       joined.Split('|').Select(s => s.Replace("||","|")).ToArray();
        // now packages[] contains the host list
    };
}

Notes:

• Lobby metadata is small and best for modest lists (tens of items).
• If payload grows large, compress it (gzip) before base64.

Use RPC when you need immediate notification or structured params.

Register and broadcast

const uint MOD = 0xDEADBEEF;

// on plugin init
IDisposable token = svc.RegisterNetworkObject(this, MOD);

// broadcast
svc.RPC(MOD, "NotifyPackages", ReliableType.Reliable,  "GAME_PACKAGES_READY");

In same class: RPC handler

[CustomRPC]
void NotifyPackages(string tag)
{
    // runs on all peers (including host by loopback)
    Logger.LogInfo($"NotifyPackages received: {tag}");
}

Notes:

• Must call PollReceive() each frame for Steam adapter.
• RegisterNetworkObject discovers methods tagged [CustomRPC].

svc.RPCTarget(MOD, "PrivateMessage", targetSteamId64, ReliableType.Reliable, "hello");

Handler:

[CustomRPC]
void PrivateMessage(string text) { Debug.Log(text); }

svc.IncomingValidator = (msg, fromSteam64) =>
{
    // drop messages with a specific method name
    if (msg.MethodName == "DropMe") return false;
    return true;
};

// Use this for unit tests or local dev when Steam not available.
INetworkingService svc = new OfflineNetworkingService();
svc.Initialize();
// Offline shim delivers messages immediately. PollReceive() is a no-op.