diff --git a/src/GmRelay.DiscordBot/Infrastructure/Discord/DiscordPlatformMessenger.cs b/src/GmRelay.DiscordBot/Infrastructure/Discord/DiscordPlatformMessenger.cs
index 3d68f36..e4ab108 100644
--- a/src/GmRelay.DiscordBot/Infrastructure/Discord/DiscordPlatformMessenger.cs
+++ b/src/GmRelay.DiscordBot/Infrastructure/Discord/DiscordPlatformMessenger.cs
@@ -51,9 +51,15 @@ public sealed class DiscordPlatformMessenger(
             });
     }
 
-    public Task SendGroupMessageAsync(PlatformGroup group, string htmlText, CancellationToken ct)
+    public async Task SendGroupMessageAsync(PlatformGroup group, string htmlText, CancellationToken ct)
     {
-        return Task.CompletedTask;
+        var channelIdStr = group.ExternalChannelId ?? group.ExternalGroupId
+            ?? throw new InvalidOperationException("Group has no ExternalChannelId or ExternalGroupId.");
+
+        if (!ulong.TryParse(channelIdStr, out var channelId))
+            throw new InvalidOperationException($"Invalid Discord channel/group ID: '{channelIdStr}'.");
+
+        await restClient.SendMessageAsync(channelId, htmlText);
     }
 
     public Task SendPrivateMessageAsync(PlatformPrivateMessage message, CancellationToken ct)