After the test has been started, and the real-time report is now available, you can copy and paste the Session ID into a document for later use (see below screenshot). This ID will be used as a parameter in the API to identify a specific session of your BlazeMeter test.

Currently, you can find the 'Session ID' in 2 ways, 

- In your Test report under the 'Original Test Configuration' report;

- During the 'Launch/Booting' page when starting your Test report.