I have variables in azure library that I want to pass to cypress so that I can have multiple stages (staging & production)

I have tried the following:

Using fixtures by having a file called environment.json that looks like so:

{
  WEB_APP_BASE_URL": "https://blight-town.com" // the "default" url for lost souls like I
}

In Azure I have a library that contains the variable ”
WEB_APP_BASE_URL” with the value “https://not-my-website.com”.

my yaml file looks so:

- task: Npm@1
                  displayName: NPM run cy:run-smoke-tests
                  inputs:
                    workingDir: 'webapp'
                    command: 'custom'
                    customCommand: 'run cy:run-smoke-tests' //this just does runs cypress for a specific spec file
                  env:
                    WEB_APP_BASE_URL: $(WEB_APP_BASE_URL)

From this was hoping to overwrite the default base url and use the value from the library but alas. Any thoughts folks?