How to debug org.elasticsearch.action.bulk .BulkRequestBuilder?

Elastic Stack Elasticsearch
4

I can't see the response.buildFailureMessage() because the application code doesn't log it. It's a reason why I am searching another way to debug.

ES cluster log files
Are not helpful. I increased logvelel to INFO (?):

curl -XPUT http://Data01:9200/_cluster/settings -d '{
    "transient" : {
        "logger.level" : "INFO"
    }
}'