SQL & PL/SQL

Hello to everyone!
I've created Oracle Autonomous DB on OCI Always Free
When I try to run following command, I receive the error “Error: cannot fetch last explain plan from PLAN_TABLE”

select * from table(dbms_xplan.display)

Error: cannot fetch last explain plan from PLAN_TABLE

I've checked the existance of Plan_table by following query, and got results as below:

SELECT
    OWNER,
    OBJECT_NAME,
    OBJECT_TYPE,
    CREATED
FROM
    ALL_OBJECTS
WHERE
    OBJECT_NAME LIKE 'PLAN_TABLE%'
    AND OWNER IN ( SYS_CONTEXT('userenv', 'current_schema'), 'PUBLIC', 'SYS' );

Thanks in advance for any help!