During the creation of a multi-domain certificate, altnames must not be indicated in the CSR. They must only be specified directly on our website interface during the certificate's creation. Note that it is possible to add or delete addresses from the certificate once it has been generated.
during the creation of your SSL certificate, only put the domain name to secure in the CN field of your CSR. The domain indicated in the CN field can not be changed later, only the altnames can be changed.
To add, modify, or delete altnames, please go to the information page for your SSL certificate, and then click on the link to regenerate the certificate.
A pop-up will open and will let you add, modify, and delete your altnames, as well as modify the CSR. Altname modifications will lead to a new round of contact and DCV verification, like during the certificate's creation.