How to get license key to use ML feature?

I install Elasticsearch, Kibana and Logstash in Ubuntu 18.04. I already used a 30-day free trial and everything went well.
Now I need the license key to continue using the ML feature in the future. But don't know to get it. I already read the document and check the pricing page (Official Elasticsearch Pricing: Elastic Cloud, Managed Elasticsearch | Elastic) but it is only for cloud version and I don't need it. How can I get the license key?

It's here Subscriptions | Elastic Stack Products & Support | Elastic also for on premise deployment
You will need to cntat Sales to get the license : Have questions? Contact Elastic | Elastic

Thanks for your answer!