v3.0 - API Tokens

You can only use API Tokens now, which you can create under My Profile / API Tokens: https://dash.cloudflare.com/profile/api-tokens. The problem with the previously used API Key is that it has global access to your Cloudflare account. With the new API Tokens, you can make the script permissions as narrow as needed.

Upgrading from earlier versions and using API Tokens is highly recommended!

The --domains option is now gone, because it made no sense (it only existed for reading from the envvar), but you can use the CLOUDFLARE_DOMAINS envvar the same as before.