Was just testing sni, also works fine.
I found 2 ways of making it work, independent of ispconfig3.
1. By adding 1 main https.vhost with all SSL hosts
2. By adding several https vhost files, 1 website per host file with include other https hosts directive.
Regarding the sni...support in ispconfig3, what system is implemented?
1. 1 main https vhost file for all websites
or like I'm guessing,
2. 1 vhost file per website (with http 80 and https 443) and include all the other https vhost files