Fix the nginx config + issue SSL certificate

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After the domain expired and was subsequently renewed, the website stopped working. The following errors occur when attempting to access via HTTPS:

ERR_SSL_VERSION_OR_CIPHER_MISMATCH (Safari, Chrome, other browsers).
ERR_CERT_COMMON_NAME_INVALID (Chrome, other browsers).
"Safari cannot open the page" (Safari).
Errors appear in the Nginx server console: no "ssl_certificate" is defined or Job for nginx.service failed.

What has been done:

The domain has been renewed.
DNS servers have been changed to Cloudflare.
Adjustments were made to the Nginx configuration, but the problem remains.
Attempts were made to reissue the Let's Encrypt certificate via AApanel, but a request limit was reached.
Currently, Nginx does not start after stopping.

Tasks to be performed:

Conduct a full server diagnosis.
Start the Nginx service.
Properly configure SSL certificates.
Configure correct operation of the Nginx + Cloudflare setup (considering errors in SSL protocols and ciphers).
Ensure full website functionality over HTTPS.
Ideally — restore website operation without waiting for restrictions from Let's Encrypt to be lifted.

Requirements for the performer:

Experience with Linux-based servers (CentOS/Ubuntu).
Confident knowledge of Nginx.
Experience with AApanel, Cloudflare, and Let's Encrypt.
Ready to start work immediately.
Ability to quickly identify and fix the cause of failure.