Fix Odoo Error & SSL

My Odoo instance is installed directly on an Ubuntu / Debian box. The site loads, but instead of the normal interface I get Odoo’s own error page. I need that application-level issue diagnosed and resolved, then I’d like the server traffic secured with a valid SSL certificate (Let’s Encrypt is fine, but I’m open to another method if you can implement it quickly and renew it automatically).

Scope
• Trace and clear the error that is blocking the interface.
• Apply and configure the SSL certificate so every request redirects cleanly to HTTPS.
• Provide a brief note of what was changed (config lines, packages, or modules) so I can maintain it later.

Acceptance
The job is complete when the site opens normally over HTTPS without warnings and no internal error pages appear during basic navigation and login tests.