Hi Federico,
With the fresh install, this included the restoring of the oracle_base.db file I presume? (Which would be correct and valid, just clarifying)
If so, you can follow the same guidance here:
TEC466528
You could (after having set the multi-currency property in the CSA to checked/true) run this command instead which essentially wraps the dbpatch command from the above tecdoc:
admin db set-multicurrency
If the multi-currency flag isn't set in the CSA then it will not generate any output (it won't run the script), if it is set, then it will invoke the dbpatch and will show you a DBTools Log output as it runs. It is no different to the dbpatch except that it first checks the CSA setting before it runs as a safeguard.
Whether using dbpatch or the admin command though, make sure the app and bg services are first stopped, and then restarted after as the tecdoc advises. If you're using a clustered environment, since this is a change to the (CSA and) DB only, you don't need to run it on each server in the cluster, just one will do. Although you most likely know this, in case any readers do not, this is an irreversible change. You can switch from Single Currency to Multi Currency but not vice versa.