RDSADMIN.RDS_FILE_UTIL.LISTDIR works from block and not in procedure

Hi gurus,

Today, I followed the instructions given in the Link: https://docs.aws.amazon.com/AmazonRDS/latest/UserGuide/oracle-s3-integration.html to perform Oracle RDS integration with S3 to import files from S3 bucket into Database directory.
I was able to perform all the steps well and able to see the files imported from my S3 bucket in the DATA_PUMP_DIR directory on the RDS instance.
When I run the query

SELECT filename FROM table(rdsadmin.rds_file_util.listdir('DATA_PUMP_DIR')) order by mtime;

Now, I am planning to get these files in a PLSQL block and the issue arises here:
When I run something like this:

DECLARE
BEGIN
  FOR fn in (SELECT * FROM table(RDSADMIN.RDS_FILE_UTIL.LISTDIR('DATA_PUMP_DIR')) order by mtime)
  LOOP
	dbms_output.put_line('File name is ' || fn.filename);
  END LOOP;  
END;

I can see the output in the dbms output window.

However, when I try to call this inside a procedure like the following:

CREATE OR REPLACE PROCEDURE test1 IS
BEGIN
  FOR fn in (SELECT * FROM table(RDSADMIN.RDS_FILE_UTIL.LISTDIR('DATA_PUMP_DIR')) order by mtime)
  LOOP
	dbms_output.put_line('File name is ' || fn.filename);
  END LOOP;  
END test1;

I receive the error:
+3/14 PL/SQL: SQL Statement ignored
3/43 PL/SQL: ORA-01031: insufficient privileges+

I searched online for this error and couldn't get any leads.
I tried writing the procedure with invoker rights

CREATE OR REPLACE PROCEDURE test1 AUTHID CURRENT_USER IS

and it still gave me the same error.

Can someone please throw light on this?

Regards,
Rakesh Devalapally