diff --git a/src/components/ClientMonitor/LabelPrinterMonitorPanel.tsx b/src/components/ClientMonitor/LabelPrinterMonitorPanel.tsx
index eb8b10d..88238a1 100644
--- a/src/components/ClientMonitor/LabelPrinterMonitorPanel.tsx
+++ b/src/components/ClientMonitor/LabelPrinterMonitorPanel.tsx
@@ -189,6 +189,11 @@ export default function LabelPrinterMonitorPanel({
         { method: "POST" },
       );
       if (checkRes.status === 401 || checkRes.status === 403) return;
+      if (checkRes.status === 404) {
+        throw new Error(
+          "標籤印表機監控 API 未啟用，請重新啟動後端並確認已部署最新版本"
+        );
+      }
       if (!checkRes.ok) {
         throw new Error(`check HTTP ${checkRes.status}`);
       }
@@ -197,7 +202,9 @@ export default function LabelPrinterMonitorPanel({
       setSummary(checkData.summary ?? null);
     } catch (e) {
       console.error("label printer monitor check", e);
-      setError("無法檢查標籤印表機狀態");
+      setError(
+        e instanceof Error ? e.message : "無法檢查標籤印表機狀態"
+      );
     } finally {
       setLoading(false);
       checkInFlightRef.current = false;
diff --git a/src/components/ClientMonitor/PrinterMonitorTab.tsx b/src/components/ClientMonitor/PrinterMonitorTab.tsx
index a07cfa3..6c2fbb5 100644
--- a/src/components/ClientMonitor/PrinterMonitorTab.tsx
+++ b/src/components/ClientMonitor/PrinterMonitorTab.tsx
@@ -85,6 +85,11 @@ export default function PrinterMonitorTab({ active, refreshAt = 0 }: Props) {
         { method: "POST" }
       );
       if (response.status === 401 || response.status === 403) return;
+      if (response.status === 404) {
+        throw new Error(
+          "印表機監控 API 未啟用，請重新啟動後端並確認已部署最新版本"
+        );
+      }
       if (!response.ok) {
         throw new Error(`HTTP ${response.status}`);
       }
@@ -94,7 +99,9 @@ export default function PrinterMonitorTab({ active, refreshAt = 0 }: Props) {
       setSummary(data.summary ?? null);
     } catch (e) {
       console.error("printer monitor check", e);
-      setError("無法檢查印表機連線");
+      setError(
+        e instanceof Error ? e.message : "無法檢查印表機連線"
+      );
     } finally {
       setLoading(false);
       inFlightRef.current = false;