Followed the documentation forsearching with raw query and it doesn't work, tried using same example with map and it did indeed work as intended. Ended up using raw query, but wrapped the json query into a poison decode.

Raw query (example from docs)
Elasticsearch.post(MyApp.ElasticsearchCluster, "/posts/_doc/_search", '{"query": {"match_all": {}}}')

Raw query (solved)
Wrap json query intoPoison.decode!
Elasticsearch.post(MyApp.ElasticsearchCluster, "/posts/_doc/_search", Poison.decode!('{"query": {"match_all": {}}}'))

I hope this helps someone.