Hey @ebalmeida,
Do you happen to have a reverse proxy (such as nginx or apache) in front of Kibana? If so, that could be rejecting the request if it's not properly configured.
If that's not the issue, you could try setting server.maxPayloadBytes to a larger value in your kibana.yml (the default value is 1048576). Settings here: https://www.elastic.co/guide/en/kibana/current/settings.html