Startsl can't generate a certificate with multi-domain support?

Question

Digital certificates

Do I understand correctly that "Free SSL Certificate - Class 1 DV SSL Certificate" allows you to add only one domain? It's confusing that they have a large field for entering domains on their site, but this is visible for Multi-domains and wildcard SSL certificates.
I tried to enter several domains, only the general one works with www, the browser swears at the rest.

Answer 1

"up to 10 domains per Certificate"
Should work for a few specific domains.
It is necessary to look at the certificate itself, what is written there.
Perhaps you are trying www.sub1.domain.ru - the certificate for sub1.domain.ru does not apply to it.

Answer 2

It no longer makes sense to generate certificates on StartSSL - Google, Apple and Mozilla have removed it (or plan to remove it soon) from their lists of root certificates.
Revoking StartCom and WoSign Root Certificate