Why is “Use environment variable” option disabled/grayed out in SSIS2012 catalog configuration?

Question

This may sound like an easy question but the answers on the net all point to the basics of setting up an environment and referencing it in the project/package.

The scena

Answer 1

Before you can map them together, you have to click References and Add the Environment that you created for that package, then it will be enabled for you.