@hevariste , There are chances that your Apache vhost configurations are not done properly.
To know about letsencrypt SSL certificate, you can follow our blog - https://cloudkul.com/blog/how-to-get-free-https-on-your-website-using-lets-encrypt-ssl/
This is a general blog to generate and configure letsencrypt free SSL for all the platforms which you can use for QloApps as well.
For your blank page issue, you check the error logs for more information about the issue.
Also, you can share your error log here as well so that we can have a look at the logs but make sure any confidential information should not visible in the screenshot, or you can blur the sensitive information from the screenshot.
If you want our team to login into your system and resolve the issue then it will be paid service and we work on an hourly support policy. We can assign our DevOps team to look into your issue.
You can create a ticket - at https://webkul.uvdesk.com/en/customer/create-ticket/ for further communications.