That website is using the Cloudflare firewall to block access (Error 1020 = Cloudflare firewall).

If you’re on a free Cloudflare account, I think you can only block based on the User Agent, and that’s available in Firewall > Tools section. You’ll have to find something unique and identifiable about the scanners and their user agents. You can see a list of Google’s bot/crawler user agents for example: Présentation du robot d'exploration Google (user-agent) | Google Search Central  |  Documentation  |  Google Developers

Pro account and above gives you many more options for the firewall.