When syncing: Replace server data or Replace local data?

• Replace Server Data: pushes your local 2Do tasks up to the sync service. Use this when 2Do has the right data and the server is empty or out of date.
• Replace Local Data: pulls tasks from the server down to this device. Use this when the server has the right data.
• Merge: reconciles both sides instead of overwriting either one, keeping items from each and only duplicating what it can't confidently match. Use this when both the device and the server hold real data you want to keep. The one-shot picker calls it Merge Sync.

Pause before choosing. If your device is empty and you choose Replace Server Data, the empty device can overwrite the cloud copy. Always pause and think about which side has the data you want to keep before confirming. When in doubt, share / export a backup first.

Where to set this any time

Beyond the automatic first-sync prompt, you can pick the next sync's behavior manually whenever you need it:

• iPhone and iPad: Settings > Sync > Next sync action.
• Mac: 2Do > Settings > Sync > Next sync action.
• Android: Settings > Sync > Next Sync Action.

Merge Sync is available for every sync method. iCloud, Dropbox, Toodledo, and CalDAV (iCloud CalDAV and custom) offer the full set: Sync Normally, Merge Sync, Replace Local Data, and Replace Server Data. WebDAV is coming soon and will offer the same set. Todoist and Apple Reminders offer Sync Normally, Merge Sync, and Replace Local Data; they never overwrite their own app's store, so Replace Server Data isn't offered for them. After the sync completes, the option resets to Sync Normally on its own.

Use Merge Sync when both sides already hold real data you want to keep, for example the first time you connect a device that already has tasks. It never deletes to make the two sides match; worst case it keeps a duplicate of an item it couldn't confidently match, which you can remove by hand. For the full description of each action, see Sync overview (Mac) or Sync overview (iOS).

Common recovery pattern

If one device has the correct 2Do data and another device is missing tasks or out of sync, use the good device as the source of truth:

1. On the device with the most accurate data, create a backup first.
2. On that same device, set Next sync action to Replace Server Data.
3. Trigger a manual sync and let it finish. This pushes that device's 2Do data up to the sync service.
4. On each out-of-sync device, set Next sync action to Replace Local Data.
5. Trigger a manual sync on each out-of-sync device. This replaces that device's local copy with the data from the sync service.

Do not choose Replace Server Data on an empty or stale device. That can overwrite the good server copy with bad data.

Syncing with Todoist or Apple Reminders?

Those two methods don't offer Replace Server Data. To push a device's data outward, run Merge Sync from the device that holds the correct data, then Replace Local Data on the others.