Xray Create sub-test execution button not displaying in Story

[Mario Elena]

Hi there, 

I had a Jira admin set up our project with Xray. 
However I notice that from the story level I cannot create a Sub-Test execution. I can create Test Executions.

I'm wondering what config am I missing ?

Looking at the docs getxray quick guide for Admin, I'm going to guess Sub-task? But I'd like to be 100% before telling our admin to make the change.