https://help.tallysolutions.com/docs/te9rel64/sync/Online_Synchronisation.htm

Online Synchronisation

In online synchronisation, the client and the server companies are connected online through the Tally.NET server or a private network. The sync rule and data are immediately transferred to the connected company for synchronisation. It is mandatory for the client and server companies need to be online during synchronisation.

To know more, click the links below:

Synchronisation via Private Network

Synchronisation via Tally.NET Server