diff --git a/elixir-phoenix/README.md b/elixir-phoenix/README.md
index 46fc9d9..ad5adbd 100644
--- a/elixir-phoenix/README.md
+++ b/elixir-phoenix/README.md
@@ -2,6 +2,9 @@
 
 - Set `Build Pack` to `nixpacks`
 - Set `MIX_ENV` to `prod`
+  - It should be a `build time` environment variable
 - Set `SECRET_KEY_BASE` to a random string (https://hexdocs.pm/phoenix/deployment.html#handling-of-your-application-secrets)
+  - It should be a `build time` environment variable
 - Set `DATABASE_URL` to your database connection string
+  - It should be a `build time` environment variable
 - Set `Ports Exposes` to `4000` (default)