OMS 13c agent installation failed with The referenced database doesn't contain a valid management Repository.

OEM 13c installation failed with The referenced database doesn't contain a valid management Repository.

This is occurring as my previous installation failed due to space issue, so there were database objects already created earlier which needs to be cleaned.

Error:

"The referenced database doesn't contain a valid management Repository."

Solution :
Properly clean the database before using it again as a OMS database :-

1. Drop sysman related schemas.

DROP USER SYSMAN CASCADE;
DROP USER SYSMAN_OPSS CASCADE;
DROP USER SYSMAN_MDS CASCADE;
DROP USER SYSMAN_APM CASCADE;
DROP USER SYSMAN_RO CASCADE;

DROP USER SYSMAN_BIPLATFORM CASCADE;

DROP USER SYSMAN_STB CASCADE;

2. Remove Synonyms related to sysman accounts :-

DECLARE
CURSOR l_syn_csr IS
    SELECT 'DROP ' ||
      CASE owner
        WHEN 'PUBLIC'
          THEN 'PUBLIC SYNONYM '
        ELSE 'SYNONYM ' || owner || '.'
      END ||
      synonym_name AS cmd
    FROM
      dba_synonyms
    WHERE
      table_owner IN (
        'SYSMAN',
        'SYSMAN_MDS',
        'MGMT_VIEW',
        'SYSMAN_BIP',
        'SYSMAN_APM',
        'BIP',
        'SYSMAN_OPSS',
        'SYSMAN_RO'
      );
BEGIN
FOR l_syn_rec IN l_syn_csr LOOP
    BEGIN
      EXECUTE IMMEDIATE l_syn_rec.cmd;
    EXCEPTION
      WHEN OTHERS THEN
        dbms_output.put_line( '===> ' || l_syn_rec.cmd );
        dbms_output.put_line( sqlerrm );
    END;
END LOOP;
END;
/

3. Removing remaining Objects and tablespaces :-

DROP USER mgmt_view CASCADE;
DROP TABLESPACE mgmt_ecm_depot_ts INCLUDING CONTENTS AND DATAFILES CASCADE CONSTRAINTS;
DROP TABLESPACE mgmt_tablespace   INCLUDING CONTENTS AND DATAFILES CASCADE CONSTRAINTS;
DROP TABLESPACE mgmt_ad4j_ts      INCLUDING CONTENTS AND DATAFILES CASCADE CONSTRAINTS;

4. As proper database cleaning using RepManager dropall didn't happen, so we have to clean up the registry details :-

DELETE
FROM
    schema_version_registry
WHERE
    (comp_name,owner) IN (
      ('Authorization Policy Manager','SYSMAN_APM'),
      ('Metadata Services','SYSMAN_MDS'),
      ('Oracle Platform Security Services','SYSMAN_OPSS')
    );
commit;

5. Retry with the installation, it should complete successfully.