I find it difficult to get full offline-mode + sync working correctly. Don't know if you have duplicates in the remote db but I think your approach has a problem: the app send the data (from scratchpad table) to server, the server saves it in DB but the connection drops on device (ex bad connection, user turn off WIFI/3G while syncing) so the app will never get a 200 response. In this case your new data was saved on server but it remains on scratchpad table. On next sync the data will be uploaded as being new: this will cause duplicates.