diff --git a/package.json b/package.json
index de80678..d8107f7 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "my-weekly-todo-list",
-  "version": "1.63.4",
+  "version": "1.63.5",
   "description": "A web-based weekly task management application that organizes to-dos and calendar events in a single, intuitive weekly view",
   "main": "index.js",
   "scripts": {
diff --git a/src/lib/outlook-calendar.ts b/src/lib/outlook-calendar.ts
index 79e511f..bdf71c4 100644
--- a/src/lib/outlook-calendar.ts
+++ b/src/lib/outlook-calendar.ts
@@ -341,44 +341,54 @@ export const updateEvent = async (
     eventId: string,
     event: any
 ) => {
-    const response = await fetch(`${GRAPH_ENDPOINT}/me/calendars/${encodeURIComponent(calendarId)}/events/${encodeURIComponent(eventId)}`, {
-        method: 'PATCH',
-        headers: {
-            'Authorization': `Bearer ${accessToken}`,
-            'Content-Type': 'application/json'
+    const body = JSON.stringify({
+        subject: event.summary,
+        body: {
+            contentType: 'HTML',
+            content: event.description || ''
         },
-        body: JSON.stringify({
-            subject: event.summary,
-            body: {
-                contentType: 'HTML',
-                content: event.description || ''
-            },
-            start: ensureTimeZone(event.start),
-            end: ensureTimeZone(event.end),
-            isAllDay: event.allDay !== undefined ? !!event.allDay : undefined,
-            location: {
-                displayName: event.location || ''
-            },
-            ...(event.recurrence ? { recurrence: event.recurrence } : {}),
-            ...(event.reminders?.length ? {
-                isReminderOn: true,
-                reminderMinutesBeforeStart: event.reminders[0].minutes,
-            } : {}),
-            ...(event.busyStatus ? { showAs: event.busyStatus === 'oof' ? 'oof' : event.busyStatus } : {}),
-            ...(event.visibility ? {
-                sensitivity: event.visibility === 'private' ? 'private'
-                    : event.visibility === 'confidential' ? 'confidential'
-                    : 'normal'
-            } : {}),
-            ...(event.attendees?.length ? {
-                attendees: event.attendees.map((a: any) => ({
-                    emailAddress: { address: a.email, name: a.displayName || a.email },
-                    type: 'required',
-                })),
-            } : {}),
-        })
+        start: ensureTimeZone(event.start),
+        end: ensureTimeZone(event.end),
+        isAllDay: event.allDay !== undefined ? !!event.allDay : undefined,
+        location: {
+            displayName: event.location || ''
+        },
+        ...(event.recurrence ? { recurrence: event.recurrence } : {}),
+        ...(event.reminders?.length ? {
+            isReminderOn: true,
+            reminderMinutesBeforeStart: event.reminders[0].minutes,
+        } : {}),
+        ...(event.busyStatus ? { showAs: event.busyStatus === 'oof' ? 'oof' : event.busyStatus } : {}),
+        ...(event.visibility ? {
+            sensitivity: event.visibility === 'private' ? 'private'
+                : event.visibility === 'confidential' ? 'confidential'
+                : 'normal'
+        } : {}),
+        ...(event.attendees?.length ? {
+            attendees: event.attendees.map((a: any) => ({
+                emailAddress: { address: a.email, name: a.displayName || a.email },
+                type: 'required',
+            })),
+        } : {}),
     });
 
+    const patchHeaders = {
+        'Authorization': `Bearer ${accessToken}`,
+        'Content-Type': 'application/json'
+    };
+
+    // Try calendar-scoped endpoint first
+    let response = await fetch(`${GRAPH_ENDPOINT}/me/calendars/${encodeURIComponent(calendarId)}/events/${encodeURIComponent(eventId)}`, {
+        method: 'PATCH', headers: patchHeaders, body
+    });
+
+    if (!response.ok && response.status === 404) {
+        // Fallback: try non-calendar-scoped endpoint
+        response = await fetch(`${GRAPH_ENDPOINT}/me/events/${encodeURIComponent(eventId)}`, {
+            method: 'PATCH', headers: patchHeaders, body
+        });
+    }
+
     if (!response.ok) {
         const err = await response.text();
         throw new Error(`Failed to update Outlook event: ${err}`);
@@ -404,13 +414,24 @@ export const deleteEvent = async (
     calendarId: string,
     eventId: string
 ) => {
-    const response = await fetch(`${GRAPH_ENDPOINT}/me/calendars/${encodeURIComponent(calendarId)}/events/${encodeURIComponent(eventId)}`, {
+    // Try calendar-scoped endpoint first
+    let response = await fetch(`${GRAPH_ENDPOINT}/me/calendars/${encodeURIComponent(calendarId)}/events/${encodeURIComponent(eventId)}`, {
         method: 'DELETE',
         headers: {
             'Authorization': `Bearer ${accessToken}`
         }
     });
 
+    if (!response.ok && response.status === 404) {
+        // Fallback: try non-calendar-scoped endpoint (works better for series master IDs)
+        response = await fetch(`${GRAPH_ENDPOINT}/me/events/${encodeURIComponent(eventId)}`, {
+            method: 'DELETE',
+            headers: {
+                'Authorization': `Bearer ${accessToken}`
+            }
+        });
+    }
+
     if (!response.ok) {
         const err = await response.text();
         throw new Error(`Failed to delete Outlook event: ${err}`);