Unable to start Elasticsearch Enterprise/App Search

Question

I've got a self-hosted Elasticsearch + Kibana environment that I'm trying to add Elasticsearch Enterprise/App Search to.

While trying to start up Elasticsearch Enterprise/App Search I'm getting the below error:

Elasticsearch API key service must be enabled. It is enabled automatically when you configure Elasticsearch to use TLS on the HTTP interface.
Alternatively, you can explicitly enable the setting within Elasticsearch by opening config/elasticsearch.yml and adding:

xpack.security.authc.api_key.enabled: true

I have added that setting and am still getting the error upon startup.

Here are the properties I modified in the elasticsearch.yml

xpac.security.enabled true
#xpack.security.audit.logfile.events.emit_request_body: true

discovery.type: single-node
xpack.security.authc.api_key.enabled: true
xpack:
  security:
    authc:
      realms:
        native:
          native1:
            order: 0