This isn't FULLY functional, but it's what I've made thus far... I'm still working on a Ice Disconnect somewhere at least for me - welcome to test.

RelayClient/ServerAPI.cs

@@ -111,6 +111,19 @@ public class ServerAPI
         var json = await response.Content.ReadAsStringAsync();
         return JsonSerializer.Deserialize<RtcDescription>(json);
     }
+    
+    public static async Task<List<string>> GetRtcParticipantsAsync(string? channelId)
+    {
+        if (string.IsNullOrWhiteSpace(channelId))
+            return new List<string>();
+
+        HttpResponseMessage response = await client.GetAsync($"api/rtc/participants/{channelId}");
+        response.EnsureSuccessStatusCode();
+
+        var json = await response.Content.ReadAsStringAsync();
+
+        return JsonSerializer.Deserialize<List<string>>(json) ?? new List<string>();
+    }
 }
 
 public class RtcDescription