diff --git a/AIStudyApp/AIStudyApp/Features/MaterialReader/ReadingEventUploadQueue.swift b/AIStudyApp/AIStudyApp/Features/MaterialReader/ReadingEventUploadQueue.swift
index 88b9018..42fba25 100644
--- a/AIStudyApp/AIStudyApp/Features/MaterialReader/ReadingEventUploadQueue.swift
+++ b/AIStudyApp/AIStudyApp/Features/MaterialReader/ReadingEventUploadQueue.swift
@@ -244,6 +244,7 @@ final class ReadingEventUploadPipeline {
             print("[UploadPipeline] Flushed \(response.processed) events")
         } catch let error as APIError {
             let errorCode = error.errorCode ?? "NETWORK_ERROR"
+            print("[UploadPipeline] APIError: statusCode=\(error.statusCode ?? -1), errorCode=\(error.errorCode ?? "nil"), message=\(error.message)")
             switch error.statusCode {
             case 401:
                 // Auth expired — keep items pending, wait for re-login