Symptoms
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A website behind Cloudflare shows the following error message in a web-browser:
ERR_TOO_MANY_REDIRECTS
The page isn’t redirecting properly
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When Cloudflare is disabled, the website loads fine.
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The Permanent SEO-safe 301 redirect from HTTP to HTTPS setting is enabled in Plesk at Domains > example.com > Hosting Settings or custom HTTPS redirection is configured in domain's .htaccess file.
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Trying to issue a Let's Encrypt certificate for the example.com domain fails with the following error:
Invalid response from https://acme-v02.api.letsencrypt.org/acme/authz-v3/11481922061.
Details:
Type: urn:ietf:params:acme:error:connection
Status: 400
Detail: Fetching /.well-known/acme-challenge/UcTI6ov0Pc3Fn2IRnNUiFKZKzBu5NaAy4IoscLbYh_I: Redirect loop detected
Cause
The SSL setting is set as "Flexible" in Cloudflare Crypto settings for this domain.
Resolution
Log in to your Cloudflare account > click the domain name > click Crypto and change the SSL setting to "Full (strict)".
Note: The Cloudflare account is created automatically during the initial activation of the extension. Since the Cloudflare extension is enabled on the server, the corresponding account on a Cloudflare side already exists. If the account credentials are forgotten, try to recover the password via the following link to access Cloudflare dashboard: https://www.cloudflare.com/a/forgot-password
The same email should be specified as for the initial extension setup.