Environment variables for one deployment
Environment variables are settings for one site: a public API base, a feature flag, a port. They are not a profile of you. Open the project and use Variables.
Add a name and a value, then save. The name is uppercase letters, digits, and underscores. The value is stored with that deployment so the site can read it when it starts.
A saved variable does not change the process that is already running. Redeploy from the Variables pane, or publish again, and the next deployment receives the new value.
You only see variables for sites on your wallet. Deleting a variable removes it from that deployment. The next deploy runs without it.