Trying to host multiple websites from single Lightsail instance

Hello.

Is it possible for you to share the web server configuration file?
Also, could you please share the directory structure up to the document root?

Just to be safe, if you are using Apache, you can distribute document roots for each domain with the following settings.
https://httpd.apache.org/docs/2.4/en/vhosts/name-based.html

<VirtualHost *:80>
    # This first-listed virtual host is also the default for *:80
    ServerName www.example.com
    ServerAlias example.com 
    DocumentRoot "/www/domain"
</VirtualHost>

<VirtualHost *:80>
    ServerName other.example.com
    DocumentRoot "/www/otherdomain"
</VirtualHost>