Thank you for your reply.
I've followed your advice but still having the same issue. Here is the error message,
"reason"=>"failed to parse date field [%{YEAR}-%{MONTHNUM}-%{MONTHDAY}] with format [strict_date_optional_time||epoch_millis]", "caused_by"=>{"type"=>"date_time_parse_exception", "reason"=>"date_time_parse_exception: Failed to parse with all enclosed parsers"}}}}}}