- Warning in browser is shown whenever the domain is accessed with www-prefix
- Let's Encrypt
- Certificate is valid and not expired
The certificate was issued only for the domain, without www-prefix.
Reissue certificate with www-prefix:
- Open Domains > example.com > Let's Encrypt
- Check the option 'Include a "www" subdomain for the domain and each selected alias'.
- Click 'Renew'.