Just because you don’t see any TXT records in your DNS records configuration does not mean they don’t exist. Because they do. You can see them here:
These records are setup by Cloudflare so they can obtain their Universal SSL Certificates for your domain. However, these records are taking precedence over the CNAME record you have configured and preventing you from getting the certificates from us.
To be clear: this is a Cloudflare restriction, there is nothing we can do from our end to fix this.
However, since you’re using Cloudflare, you don’t really need a custom SSL certificate either. We provide a self-signed certificate by default which is sufficient for Cloudflare’s Full SSL mode: