Apache: two domains on the same server with different ports - apache

Question

I'm newbie on this stuff so forgive me if i'm doing a stupid question. I have a vue application running on port 80 working just fine over SSL (say www.domain.com and domain.com).
Now I need my springboot application, which is running over port 8443 to be accessible by a secure connection too (say on api.domain.com) but i can't quite figure what i'm doing wrong...
I can access the api if i'm not including the second virtualhost, but only using http... Also, when I just type api.domain.com it goes to domain.com start page too. And when I include the second virtualhost, I can't even acces domain.com.
<IfModule mod_ssl.c>
<VirtualHost *:443>
ServerAdmin webmaster#localhost
DocumentRoot /var/www/html
ErrorLog ${APACHE_LOG_DIR}/error.log
CustomLog ${APACHE_LOG_DIR}/access.log combined
ServerName www.domain.com
Include /etc/letsencrypt/options-ssl-apache.conf
ServerAlias domain.com
ProxyPreserveHost On
SSLCertificateFile /etc/letsencrypt/live/domain.com/fullchain.pem
SSLCertificateKeyFile /etc/letsencrypt/live/domain.com/privkey.pem
</VirtualHost>
<VirtualHost *:443>
ServerAdmin webmaster#localhost
ServerName api.domain.com
Include /etc/letsencrypt/options-ssl-apache.conf
ServerAlias api.domain.com
SSLCertificateFile /etc/letsencrypt/live/domain.com/fullchain.pem
SSLCertificateKeyFile /etc/letsencrypt/live/domain.com/privkey.pem
ProxyPreserveHost On
ProxyPass / http://127.0.0.1:8443/
ProxyPassReverse / http://127.0.0.1:8443/
</VirtualHost>
</IfModule>

Answer 1

Found it out: there are some apache modules that need to be activated. Just did it with
sudo a2enmod proxy
sudo a2enmod proxy_http
and everything works like a charm.