Hi @blenolopes,
I think the cause might be that "message" uses the standard analyzer which by default which
strips the = symbol. More about analyzers you can read here: https://www.elastic.co/guide/en/elasticsearch/reference/current/analysis-analyzers.html
Here's the post with similar problem to yours and a set of steps that could help you (in response):
How to Index special characters and Search those special characters in Elasticsearch