I'm trying to add a subdomain to my Wordpress website that I host through Wordpress. The ConvertKit troubleshooting article says, "In your DNS records, make sure that you have no other A records or AAAA records present. If you do have any other A or AAAA records present, they will need to be removed before you can use your custom domain with ConvertKit." But my main domain is an A record. How can I make this work?