settings_exception: Invalid settings

What does it mean?

The operation was rejected because the given setting is invalid. While applying index or cluster settings, there is a problem with the setting name, its value, or whether it can be changed in that context.

Why does it happen?

An unknown/misspelled setting name; a value of the wrong type or outside the allowed range; trying to change on a live index a static setting that can only be set at index creation (e.g. number_of_shards); or using a removed/renamed setting.

How to fix it

Validate the setting name and value against the documentation. Update dynamic settings on the live index: PUT my-index/_settings {"index.number_of_replicas": 2}. Static settings (e.g. number_of_shards) are set only at creation; changing them requires a reindex. View current settings: GET my-index/_settings.