If you use Cloudflare as a proxy and receive an error about too many redirects (redirect loop) when accessing your domain, this is due to faulty communication between Cloudflare and your web server. Usually, your server enforces a secure connection, while Cloudflare tries to retrieve the data unencrypted.Cause of the problemThe error usually occurs because of the Cloudflare setting Flexible. In this mode, Cloudflare contacts your server over the unencrypted HTTP protocol. However, since your server is configured to redirect all requests to HTTPS, it sends Cloudflare back to the encrypted version. Cloudflare then requests again via HTTP, which triggers the redirect loop.Step-by-step guide to fixYou need to instruct Cloudflare to establish a secure connection to your origin server to comply with your server's security rules.Log in to your Cloudflare Dashboard.Select the affected domain.Click on SSL/TLS » Overview in the left sidebar.Check the current encryption mode. It is likely set to Flexible.Change the setting to Full or Full (St...

You receive the security warning because for subdomains that serve as redirect domains after the change, technically no SSL certificates are delivered anymore, even if one existed before the switch. The redirect from the old domain including https:// therefore fails or leads to the security warning, as the certificate is only issued for the active main domain.The main system only delivers the SSL certificate for the active main domain (domainNEU.tld). Subdomains (domainALT.tld) do redirect to the main domain but no longer receive their own SSL certificate, which causes the security warning at https://domainALT.tld.Working redirect examples (without explicit HTTPS)The following calls correctly redirect to the new main domain:domainALT.tldwww.domainALT.tlddomainALT.tld/pfad/http://domainALT.tldhttp://www.domainALT.tldhttp://domainALT.tld/pfad/Non-working redirect examples (with explicit HTTPS)The following calls show the security warning because no valid SSL certificate is delivered for the old domain:https://domainALT.tldhttps://www...