---
title: "Sync Troubleshooting FAQ"
description: "Calendar synchronization issues can occasionally occur due to expired security tokens, revoked calendar permissions, network disruptions, or account connection warnings. When synchronization fails,..."
last_updated: "2026-10-18T15:43:01.206618+00:00"
canonical_url: "https://docs.calendar0.app/guide/troubleshooting/sync-troubleshooting-faq"
---

## Overview

Calendar synchronization issues can occasionally occur due to expired security tokens, revoked calendar permissions, network disruptions, or account connection warnings. When synchronization fails, you might notice missing calendar events, sync error alerts in your dashboard, or banners indicating that an account needs attention. 

Supported calendar providers: Google, Microsoft, Apple.

> [!NOTE]
> Disconnecting or reconnecting your calendar accounts only affects how they appear within the software. Your actual calendar data stored with your provider remains completely safe and untouched.

---

## Troubleshooting Common Sync Failures

### 1. Account Connection Warnings and Expired Permissions

When security tokens expire or permissions are revoked, the software displays an alert banner prompting you to reconnect your account.

1. Navigate to your **Settings** and select the **Accounts** tab.
2. Locate the affected account entry displaying a warning or error badge.
3. Click the **Reconnect** button next to the account email address.
4. Follow the provider sign-in steps to re-authorize calendar access.

> [!IMPORTANT]
> For Google accounts, ensure you grant all requested calendar read and write permissions during the authorization prompt. If calendar permissions are unticked on the consent screen, synchronization will fail.

### 2. Apple Calendar App-Specific Password Errors

Apple accounts do not use standard web pop-up logins. Instead, they require an app-specific password generated directly from Apple.

1. Go to the Apple account management website (`account.apple.com`) and sign in.
2. Navigate to the **Sign-In and Security** section.
3. Generate a new app-specific password.
4. Open the app settings, click **Reconnect** or add your Apple Calendar account, and paste the newly generated app-specific password alongside your Apple ID email.

> [!WARNING]
> Do not use your standard Apple ID login password. Apple CalDAV integrations require an app-specific password to authenticate successfully.

### 3. Browser Pop-Up Blocked During Connection

If you attempt to connect a Google or Microsoft account and nothing happens, your web browser may be blocking the authentication window.

1. Look for a pop-up blocked icon in your browser's address bar.
2. Change your browser settings to allow pop-ups and redirects for this website.
3. Try connecting your calendar account again.

---

## Connection Failure Reference

When establishing or maintaining a connection, you may encounter specific status messages indicating why a connection failed.

| Failure Type | Description | Recommended Action |
| :--- | :--- | :--- |
| `access_denied` | Calendar permissions were denied or unticked during sign-in. | Try connecting again and explicitly allow calendar access. |
| `popup_blocked` | The browser prevented the authentication window from opening. | Allow pop-ups for this site in your browser settings and retry. |
| `state_mismatch` | The sign-in session expired or timed out. | Retry the sign-in process immediately. |
| `network` | The application could not reach the calendar servers. | Check your internet connection and try again. |
| `unavailable` | The calendar provider is temporarily down or unreachable. | Wait a minute and try connecting again. |

---

## Account Health Troubleshooting Workflow

The system periodically probes account health to verify that credentials remain valid. Use the flowchart below to understand how the system detects and resolves sync health issues:

```mermaid
flowchart TD
    A[Account Health Check] --> B{Are tokens valid?}
    B -->|Yes| C[Account Healthy — Sync Active]
    B -->|No| D{Is it a Reconnect Error?}
    D -->|Yes| E[Show Reconnect Warning Banner]
    D -->|No| F[Temporary Outage — Auto-retries]
    E --> G[User Clicks Reconnect & Authenticates]
    G --> C
```

> [!TIP]
> If you experience stubborn synchronization delays, you can force a manual refresh by navigating to your calendar view or resetting the query cache via your account settings.

## Related

- [Connecting Calendar Accounts](https://docs.calendar0.app/guide/integrations/connecting-calendar-accounts)
- [Calendar Views Events](https://docs.calendar0.app/guide/core-features/calendar-views-events)


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