Update: Edited to change JSON formatting.

RelayServer/Endpoints/RtcEndpoints.cs

@@ -28,7 +28,8 @@ public static class RtcEndpoints
         // Return whether the specified channel currently has an active call.
         app.MapGet("/api/rtc/active/{channelId}", async (string channelId, RtcCallService rtcCallService) =>
         {
-            return Results.Ok(await rtcCallService.HasActiveCallAsync(channelId));
+            var call = await rtcCallService.GetActiveCallAsync(channelId);
+            return call is null ? Results.NotFound() : Results.Ok(call);
         });
 
         // Return the latest stored SDP offer for the specified channel.