I am creating an app using Symfony 4 and Docker. In my .env file, I have the following line: 

```
DEVICE_CREATION_SECRET=123456

```

... and in my services.yaml file, I have the following definition:

```
VMS\Application\DigitalRetail\Handler\DeviceForwardHandler:
    arguments:
        - env(DEVICE_CREATION_SECRET)

```

... which I expect to hand off my secret (123456) to my class, since I have this in that class:

```
public function __construct(string $deviceCreationSecret)
{
    $this->deviceCreationSecret = $deviceCreationSecret;
}

```

But when I run my app and dump out the value, I get `env(DEVICE_CREATION_SECRET)` rather then my secret (123456). What do I need to get access to that secret?