My domain is: madingxiaowei.ddns.net.
I wanted to renew my cetrificate. Below you’ll find the output. I guess something is wrong with my apache server. But I don’t know what. I haven’t changed anything in my apache configuration 
A test file at https://madingxiaowei.ddns.net/.well-known/acme-challenge/test.txt is found and there is no redirection.
I ran this command: sudo ./certbot-auto renew
It produced this output:
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Processing /etc/letsencrypt/renewal/madingxiaowei.ddns.net.conf
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Cert is due for renewal, auto-renewing...
Plugins selected: Authenticator apache, Installer apache
Renewing an existing certificate
Performing the following challenges:
http-01 challenge for madingxiaowei.ddns.net
Waiting for verification...
Cleaning up challenges
Attempting to renew cert (madingxiaowei.ddns.net) from /etc/letsencrypt/renewal/madingxiaowei.ddns.net.conf produced an unexpected error: Failed authorization procedure. madingxiaowei.ddns.net (http-01): urn:ietf:params:acme:error:unauthorized :: The client lacks sufficient authorization :: Invalid response from http://madingxiaowei.ddns.net/.well-known/acme-challenge/m4HFhMbmK-NA0xIHhm1ESmWU0RYYTHBvTlIZWcy2yS0: "<?xml version=\"1.0\" encoding=\"iso-8859-1\"?>\n<!DOCTYPE html PUBLIC \"-//W3C//DTD XHTML 1.0 Transitional//EN\"\n \"http://www.". Skipping.
All renewal attempts failed. The following certs could not be renewed:
/etc/letsencrypt/live/madingxiaowei.ddns.net/fullchain.pem (failure)
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All renewal attempts failed. The following certs could not be renewed:
/etc/letsencrypt/live/madingxiaowei.ddns.net/fullchain.pem (failure)
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1 renew failure(s), 0 parse failure(s)
IMPORTANT NOTES:
- The following errors were reported by the server:
Domain: madingxiaowei.ddns.net
Type: unauthorized
Detail: Invalid response from
http://madingxiaowei.ddns.net/.well-known/acme-challenge/m4HFhMbmK-NA0xIHhm1ESmWU0RYYTHBvTlIZWcy2yS0:
"<?xml version=\"1.0\" encoding=\"iso-8859-1\"?>\n<!DOCTYPE html
PUBLIC \"-//W3C//DTD XHTML 1.0 Transitional//EN\"\n
\"http://www."
To fix these errors, please make sure that your domain name was
entered correctly and the DNS A/AAAA record(s) for that domain
contain(s) the right IP address.
My web server is (include version): apache 2.4.10
The operating system my web server runs on is (include version): raspbian stretch
My hosting provider, if applicable, is: n/a
I can login to a root shell on my machine (yes or no, or I don’t know): yes
I’m using a control panel to manage my site (no, or provide the name and version of the control panel): no
Help is highly appreciated! Thx.
Martin