I think you may have extra spaces when entering the domain name
I have same prob also with a domain what not proxied by cloudflare.
A record must fill in mail.ixnoc.com or the other like aaaa.ixnoc.com
I get this error when trying to configure with cloudflare
Hello, there is no A record found for mail at present, try to add it again, change the auto to 1 minute, and then try again later?