Region must be a valid RFC host label.

When I run a command calling the S3 add-on, I get the following error:

```
Aws\Exception\InvalidRegionException
Region must be a valid RFC host label.
```

This comes from `throw new InvalidRegionException('Region must be a valid RFC'` in `wp2static-addon-s3/vendor/aws/aws-sdk-php/src/ClientResolver.php`

My region is set to `eu-west-2`

Do you know why this error is thrown?