Bamboo CI integration - What is a build key?

Hi, I’m following the tutorial to configure Bamboo with Gitlab.

"Enter the build key from your Bamboo build plan"

I’m using Bamboo 6, but I cannot observe something called “build key”.

This is the screen when I’m trying to create a build plan.

What is the “build key” referring; Project key or Plan key?

-Best Regards

Plan key, you can also see it in the url as a query param once you create the plan and focus the “plan configuration” section