Unfortunately Amazon RDS for Oracle RDS doesn't supply SYSDBA privileges.
In our documentation we advise that you must set the following Execute Right:
GRANT execute ON dbms_lock TO <user>
This right can only be set by a user who has the SYSDBA privilege.
Amazon; documents that they don't supply this right:https://docs.amazonaws.cn/en_us/AmazonRDS/latest/UserGuide/Oracle.Procedural.Importing.html
and therefore we unfortunately cannot support this environment.