Issue letsencrypt help one ip two domain, can't figure it out

[joeblow]

plesk on windows 2019 server, named server.domain1.com. domain 1 created, named domain1.com on shared primary ip. letsencrypt ssl created, secures plesk (server.domain1.com) and domain1.com. works.

then, domain2.com is created on same shared primary ip. letsencrypt ssl created and deployed on domain 2. sslab test passes cert 1, but cert #2 throws "no sni" and "alternate name server.domain1.com mismatch".

why is server.domain1.com showing up in this test when it's not in the ssl i'm testing? if the answer is enable sni, isn't sni enabled on windows by default? if not, how do i enable it and where in plesk/letsencrypt/windows? if sni isn't the fix, what is? how do you use letsencrypt to create multiple ssls on multiple domains using one shared ip in plesk?

please explain as if i'm a child.