The value field contains the CA domain name. This field can contain the name of a CA other than an Amazon CA. However, if you do not have a CAA record that specifies one of the following four Amazon CAs, ACM cannot issue a certificate to your domain or subdomain:

amazon.com

amazontrust.com

awstrust.com

amazonaws.com

The value field can also contain a semicolon (;) to indicate that no CA should be permitted to issue a certificate for your domain or subdomain. Use this field if you decide at some point that you no longer want a certificate issued for a particular domain.