CPanel shared hosting with multiple domains

You can test how domains work on your hosting provider by creating a subdomain. Usually the cpanel will have an option for creating it where you can specify which will be its public_html (and its respective name) directory. You could then place your codeigniter directories within/alongside it and place your vendor/, composer.json and composer.lck one directory higher, producing the following structure:

/php
/public_ftp
/public_html
/main-domain
/ssl
/subdomain.yourdomain.com/app
/subdomain.yourdomain.com/public
/subdomain.yourdomain.com/writable
/subdomain.yourdomain.com/spark
/subdomain.yourdomain.com/.env
/vendor
/composer.json
/composer.lck

More information in the docs: 

• Deployment to Shared Hosting Services
  
• Running Multiple Applications with one CodeIgniter Installation
  

The directory structure you have employed leads me to believe the sites are not separate domains, rather they are subdirectories inside your main domain. So you could see all of them in a list if you accessed http://main-domain/ and you could travel to each by doing http://main-domain/domain1, http://main-domain/domain2, etc. Not sure what your level of server admin is, but you may want to brush up on how to configure your hosting. Of course that may also be how you want your sites set up, but that seems suspect.

Halberd | CodeIgniter Sandbox