SSMS Linked Server -ORA-28009: connection as SYS should be as SYSDBA or SYSOPER (Microsoft SQL Server, Error: 7303)
I found the problem and you can follow my steps to fix this issue.
1. Don't use SYS to be your USERID
2. Add new USERID

-- CREATE USER SQL
1. CREATE USER a
2. IDENTIFIED BY a
3. DEFAULT TABLESPACE "USERS"
4. TEMPORARY TABLESPACE "TEMP";
*** &lt;-- if you got the error, please follow above content to fix problem
 (SQL&gt; alter session set "_ORACLE_SCRIPT"=true;  )
-- ROLES
GRANT DBA TO a;