Hey @TanguyLauc, the Sandbox in SDK 2.x is based on Canton which sets the ledger id to the participant id rather than letting you configure it separately, see Canton: how to set participant's ledger id - #3 by Ratko_Veprek.
As described in Daml Sandbox — Daml SDK 2.1.1 documentation the participant used when you spawn daml sandbox is called sandbox so that will also be your ledger id.
Do you have a specific reason why you’re trying to change the ledger id?