Where is subscription Key

I am following the exercise

Exercise: Create a backend API at

https://learn.microsoft.com/en-us/training/modules/explore-api-management/8-import-api

In step

it is showed or not indicated to check "Subscription Required" however, in the test stage, step 2, it says

The Ocp-Apim-Subscription-Key is filled in automatically for the subscription key associated with this API

which is not true as you can notice in the my API snapshot

How come that it is generated, we dont see it anywhere and is bound to the API? Is it a mistake from the author?