Make sure you click the Add button to add the parameter to the list. If you do not click the add button, the parameter is not registered and will not be added.
This does not work because the syntax is invalid.
The easiest way to test that environment variables are being automatically injected into your pipeline is to run the env command which will demonstrate the parameter was properly added, as show in this example:
kind: pipeline
type: docker
name: default
steps:
- name: test
image: alpine
commands:
- env