Database syncing is supported in the PRO version, and previously via one of two in-app purchases: Personal Sync (iCloud) and Family Sync (Dropbox). If needed, purchases can be restored by turning on the Syncing switch on the Settings screen.
In the Backups and Syncing section, first ensure iCloud is enabled, or iCloud is disabled and Dropbox enabled (if you prefer to use Dropbox). Then enable Syncing.
Syncing requires you to identify one PRIMARY device and one or more SECONDARY devices (up to 9 in fact). It doesn’t really matter which is PRIMARY, as long as it has your most up-to-date data!
On your PRIMARY device, enable syncing. On each of your SECONDARY devices, do the same. If it only gives you the option of being the PRIMARY, select Cancel and try again. It can take a while for your PRIMARY to become visible.
Your SECONDARY will then wait to get an initial sync from the PRIMARY device. Make sure your PRIMARY is running, and give it time (up to a minute or so, even on WiFi). The initial sync will OVERWRITE the data on the SECONDARY, making sure the two devices start off with the same data.
With syncing enabled, any changes to your accounts, budgets, groups and transactions will be saved and passed to other devices when you close the app.
If a change is detected on any other device, you will be notified via a red Sync button on the Settings tab at the bottom right of the screen. Simply select this and confirm to merge changes. I could do this all automatically, but it is nice to know when a change has happened, especially for Family Sync.
To view changes and who made them (i.e. which device), tap the Help button at the top left of the Settings screen and choose Sync Log.
To disable syncing on a SECONDARY device, simply turn it off in the settings. If you do this on your PRIMARY device, syncing is disabled on all devices. If your PRIMARY device is unavailable (e.g. lost), you can disable syncing on ALL devices from any SECONDARY by enabling syncing and selecting Reset.
Changes are only written when you close the app (by pressing the home button). This is not really a restriction, it is a design choice to reduce the amount of data you are copying around.
Changes to your account order, group order and your settings are NOT synced.
Deleting an account is also NOT synced, mainly because this is a dangerous operation (all related transactions are deleted too). The same applies to deleting groups. If you want to delete an account or group, you will need to do this separately on each device.
While changes are timestamped and applied in the correct order, the granularity is at the account, the main (all accounts) budgets, the group and the transaction level. If two devices make changes to the same object, the latter change will always win (unless a sync happens in between). Note that a recurring transaction and all its occurrences is one object.
Changes are only made available for 92 days (3 months), so if a device has been offline for longer than this, I recommend disabling and re-enabling syncing.