# `configuration.binding_invalid`

Setting names a variable that is not in capitals.

Area 10, [Configuration and time](../topics/configuration-and-time.md); not declinable; the next step is usually the agent's.

```jadpo
config {
    mail_sender: Email {
        binding: "MAIL-SENDER"
    }
}
```

```text
error: `MAIL-SENDER` can't be a variable name
 --> main.jadpo:3:18
  |
3 |         binding: "MAIL-SENDER"
  |                  ^^^^^^^^^^^^^ not a variable name
  reason: A variable name is capital letters, digits and `_`, starting with a capital letter, so every platform accepts it.
  next: Use `MAIL_SENDER` (agent)
  rule: configuration.binding_invalid
  help: https://jadpo.dev/docs/errors/configuration.binding_invalid

check failed: 1 error, 1 file
```