Multi-domain certificates can only be renewed with the same number of SANs (additional domains). There is no option to change the number of additional domains during checkout. However, there are two ways to add more additional domains to the renewal certificate:
- purchase additional domains before activating the renewal certificate;
- activate the renewal certificate and purchase more slots during reissue.
Additional domains can be purchased from your SSL list > click on the certificate ID > click on "Add more" button in the "Secures X of 100 domains" line.