Let's Encrypt failing to authenticate

Let’s Encrypt is failing to authenticate a certificate and I don’t understand the error:

Certbot failed to authenticate some domains (authenticator: apache). The Certificate Authority reported these problems:
Domain: rt.deepsoft.com
Type: unauthorized
Detail: 108.161.129.198: Invalid response from Login “\n\n\n<html lang="en">\n \n Login\n <meta http-equiv="X-UA-Compatible" content="IE=edge" />”