Why is my Vercel production deployment still using an old environment variable value?

That usually means the live deployment was built before you changed the variable. Vercel applies env-var changes only to new deployments, so first make sure you edited the value for the Production environment, then trigger a fresh production deployment from the production branch (or deploy with `vercel --prod`). Also double-check you aren't testing an older deployment URL—those keep the values they were built with. If it still looks wrong, compare Production with Preview/Development and any branch-specific overrides; it's pretty easy to update the right name in the wrong environment.