我是 Linux 新手，使用以下指南来使用反向代理（因为其他指南要求它），但是当像下面这样为 certbot 发出命令时，它显示错误，屏幕上显示的内容在这里，请指导并帮助解决问题。
指南链接： https://linuxize.com/post/secure-nginx-with-let-s-encrypt-on-ubuntu-16-04/
发出命令：
sudo certbot certonly --agree-tos --email [email protected] --webroot -w /var/lib/letsencrypt/ -d example.com -d www.example.com
屏幕输出：
Saving debug log to /var/log/letsencrypt/letsencrypt.log
Plugins selected: Authenticator webroot, Installer None
Obtaining a new certificate
Performing the following challenges:
http-01 challenge for example.com
http-01 challenge for www.example.com
Using the webroot path /var/lib/letsencrypt for all unmatched domains.
Waiting for verification...
Cleaning up challenges
Failed authorization procedure. www.example.com (http-01): urn:ietf:params:acme:error:unauthorized :: The client lacks sufficient authorization :: Invalid response from http://www.example.com/.well-known/acme-challenge/ameVqhIT7MDOLg14nyeds58FskkEdJgQVML0tvy9d5E [2606:2800:220:1:248:1893:25c8:1946]: "<!doctype html>\n<html>\n<head>\n <title>Example Domain</title>\n\n <meta charset=\"utf-8\" />\n <meta http-equiv=\"Content-type", example.com (http-01): urn:ietf:params:acme:error:unauthorized :: The client lacks sufficient authorization :: Invalid response from http://example.com/.well-known/acme-challenge/HP2HDgSV7StnrURJnzMfnb0_pMabrWbd3wfquqpfHsA [2606:2800:220:1:248:1893:25c8:1946]: "<!doctype html>\n<html>\n<head>\n <title>Example Domain</title>\n\n <meta charset=\"utf-8\" />\n <meta http-equiv=\"Content-type"
IMPORTANT NOTES:
- The following errors were reported by the server:
Domain: www.example.com
Type: unauthorized
Detail: Invalid response from
http://www.example.com/.well-known/acme-challenge/ameVqhIT7MDOLg14nyeds58FskkEdJgQVML0tvy9d5E
[2606:2800:220:1:248:1893:25c8:1946]: "<!doctype
html>\n<html>\n<head>\n <title>Example Domain</title>\n\n
<meta charset=\"utf-8\" />\n <meta http-equiv=\"Content-type"
Domain: example.com
Type: unauthorized
Detail: Invalid response from
http://example.com/.well-known/acme-challenge/HP2HDgSV7StnrURJnzMfnb0_pMabrWbd3wfquqpfHsA
[2606:2800:220:1:248:1893:25c8:1946]: "<!doctype
html>\n<html>\n<head>\n <title>Example Domain</title>\n\n
<meta charset=\"utf-8\" />\n <meta http-equiv=\"Content-type"
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.