In contrast to a website, GTO allows you to manage your task list even when an internet connection isn't available. Periodically, though, it needs to sync with the Google Task servers - i.e. it sends the changes made in GTO, and retrieves the changes made outside GTO, so that both versions of your lists stay updated.
Each sync consumes a small amount of battery and network data usage. For this reason, constantly syncing with the server is not viable, as it would quickly drain the battery, and possibly take a large chunk of the monthly data quota. Instead, GTO syncs automatically at regular intervals, and when you request a sync. With periodic syncing, the impact on battery and data is usually very low compared to other common Android apps.
When you change a task or a list in GTO, that change is quickly sent to the server. This is much faster than performing a full sync for every change, since only one short message needs to be sent over the network. You can choose to disable instant sending through the Server Sync settings.
Full syncs - in which GTO retrieves changes from the server, and sends any local changes that weren't already sent - occur automatically throughout the day, and can be triggered manually.
To start a full sync, open the GTO Menu and select Sync All. The title bar at the top of the screen will show the sync's progress. Lists that have been changed since the previous full sync will be downloaded from the server. This includes changes that were made in GTO. Lists that haven't changed are skipped.
The interval at which full syncs occur automatically can be changed through the Full Sync Frequency preference. After a successful full sync, GTO will wait for the chosen interval. Then it will attempt to open a network connection and start syncing. However, there are several things that might prevent GTO from syncing at the expected time. See the troubleshooting section below for more information.
If you're having problems pushing your tasks to the Android calendar, please try the suggestions on the FAQ page and on the Google support site.
Occasionally GTO will run into a problem trying to sync. The most common cause is an unstable internet connection. Make sure that your device is connected to a WiFi or cellular data network, and that it's not behind a firewall or proxy server preventing the connection.
Network connection problems can sometimes also be fixed by rebooting the device. If GTO seems to be the only app affected, try going to the system settings applications page for GTO, and select Force Stop.
When GTO tries to perform an automatic sync and it isn't able to connect to the internet, it will try a few more times and then wait for the next automatic interval. Each time GTO is opened, it checks to see when the previous successful sync occurred. If it's been longer than the expected interval, it will try syncing as soon as the app is opened.
If Android asks for your account password every time GTO syncs, it's probably because 2-step verification is enabled on your account. Follow the instructions on Google's 2-step verification help page for signing in with an app-specific password.
You can change whether GTO notifies you of sync errors through the Dialogs preference menu.
If you get a 503 error, that means the server is having temporary issues. Try syncing again in 15 minutes.
If GTO keeps getting errors every time it syncs and no other solutions seem to be working, it might help to re-import the account into GTO. First, make sure your tasks are up to date in GMail, since this process will remove any unsynced tasks from GTO. If your lists and tasks are correct online, go to the GTO Menu > Settings > Edit Accounts, uncheck your account name, select Delete, then re-check your account name.