Set Parameter in SPFILE still outputs the same error

for the installation of a SAP IDM system, I need to know how to use the command alter system set "_ORACLE_SCRIPT"=true SCOPE=SPFILE; command correctly. The installation creates a user and gives the error ORA-65096: "invalid common user or role name". During the researches I found the command alter session set "_ORACLE_SCRIPT"=true. This command allows to create users temporarly. At the next session or in a separate terminal, this is no longer possible. In the $ORACLE_HOME/dbs/spfile.ora the parameter *_oracle_script=true was in there, but it gives me the same error again. Thank you in advance. -Sruscht