Hello Pirmin,
I see you got no response from BT directly so here some advice from Partner to Partner.
You can start sessions with the client scripting, leveraging the BRCS File
https://docs.beyondtrust.com/pra/reference/client-scripting-api
Here an extract of the Docs:
This can be done from the installed Access console for example :
bomgar-acc.exe --run-script "action=start_jump_item_session&client.hostname=ABCEF02&session.custom.external_key=123456789" bomgar-acc.exe --run-script-file my_script_file.brcs-beta60
Or directly with the scripting API URL : https://access.example.com/api/client_script
This API accepts a client type (rep), an operation to perform (generate), a command to put in the script file, and a set of parameters to pass to the command. Here is an example of a valid Client Scripting API request:
https://access.example.com/api/client_script?type=rep&operation=generate&action=start_jump_item_session&client.hostname=ABCDEFG02
When using the start_jump_item_session command this should work for TCP and Network Tunnels as well.
I hope this helps to guide you in the right direction.
Best Regards,
Jess