Currently I have researched my problem but I can not find any solution for my second domain, I have not been able to make the wildcard certificate work with the additional domain added to MULTI-DOMAINS.
To start, the main site has its dedicated ip and works well here you can see it https://18.104.22.168
Currently the main site has a ssl wildcard by DigiCert Inc and is working correctly when new sub sites are created under https://page.mainsite.com everything runs fine.
Now I took the seconddomain.com with the same nameservers of the hosting account and I made it available as Addon Domains through the cpanel of the mainsite.com
then I create a wildcard A record in your DNS zone editor and point it to the dedicated IP of the mainsite.com ass you says in the plugin usage section.
after that install a new wildcard certificate for the seconddomain.com by GlobalSign nv-sa and I install it via cpanel through the SSL / TLS option
Now I do not know where the problem is, because through wordpress when I create a new sub site using the second domain using MULTI-DOMAINS plugin the htpps: // throw error does not work
But if I create a sub domain using the cpanel of mainsite.com but selecting the seconddomain.com like page.seconddomain.com then it works without problems.
The question is, should I set up the second domain in a real hosting account with another different dedicated ip from mainsite.com? it's the only thing I need to solve to finish my project and I'm stuck with a lot of headaches.
I hope this post will be useful for future generations, thanks!!!