TSA, or time stamp service, is a solution that proves that certain data existed at a given point in time.
Under DigiDoc4 Client settings it is possible to set access to the Time-Stamping service.
To set a Time-Stamping service URL:
1. Launch the DigiDoc4 Client application.
2. Open at the top right "Settings".
3. Under Settings, select "SERVICES".

4. Set the TSA URL in the "Access to Time-Stamping service" box.
Authorities can also set the Time-Stamping service URL via registry. More information about registry parameters can be found here.