Oracle Message ORA-16217 - prepare to switchover has not completed

ERRORprepare to switchover has not completed
CAUSEAn ALTER DATABASE PREPARE TO SWITCHOVER command was issued, but the prepare activity did not complete.
ACTIONVerify that the standby was prepared properly. You may cancel the prepare and perform an unprepared switchover which requires a database link to complete. Or reissue the prepare operation on the standby.