ORA-29861: domain index is marked LOADING/FAILED/UNUSABLE

1. Run the Below Script

SELECT OWNER, INDEX_NAME, INDEX_TYPE, STATUS, DOMIDX_STATUS, DOMIDX_OPSTATUS ,TABLE_NAME FROM DBA_INDEXES
WHERE INDEX_TYPE='DOMAIN'
AND INDEX_NAME LIKE 'HZ%'

the result of the above query will be

OWNER    INDEX_NAME    INDEX_TYPE    STATUS    DOMIDX_STATUS    DOMIDX_OPSTATUS    TABLE_NAME

AR    HZ_STAGE_PARTIES_T1    DOMAIN    VALID    VALID    FAILED    HZ_STAGED_PARTIES

2. Drop the Invalid Index.

3. Create script as mentioned below

CREATE INDEX AR.HZ_STAGE_CONTACT_T1 ON AR.HZ_STAGED_CONTACTS
    (CONCAT_COL) INDEXTYPE IS CTXSYS.CONTEXT

It will resolve the ORA-29861