How to avoid ORA-38726 error

You should always verifiy that flashback logging is enabled before you create a restore point.

SQL> select FLASHBACK_ON from v$database;

FLASHBACK_ON
------------------
NO

To enable flashback logging, database must be in archive log mode, else you will get this error

ERROR at line 1:
ORA-38706: Cannot turn on FLASHBACK DATABASE logging.
ORA-38707: Media recovery is not enabled.

So you will need to enable it

shutdown immediate;

startup mount;

alter database archivelog;

alter database flashback on;

alter database open;