Ubuntu 20.04 LTS服务器绑定Ubuntu Pro账户失败，证书验证报错求助

各位好，我碰到个棘手的问题想请教大家：我们的托管服务商刚搭建了一台Ubuntu 20.04 LTS服务器，我需要给这台机器应用CIS基准配置的Level 1 Server profile。我自己有Ubuntu Pro账户，于是尝试用sudo pro attach <我的实际Token>命令绑定服务器，但一直失败，报错信息是：

Failed to attach machine. see Ubuntu Pro控制台页面

我已经试过几个排查方法，比如参考过AskUbuntu上的相关问题，还运行了sudo curl -vs Canonical合约服务地址来测试网络连接，输出如下：

Trying 185.125.190.31:443...
TCP_NODELAY set
Connected to contracts.canonical.com (185.125.190.31) port 443 (#0)
ALPN, offering h2
ALPN, offering http/1.1
successfully set certificate verify locations:
CAfile: /etc/ssl/certs/ca-certificates.crt
CApath: /etc/ssl/certs
TLSv1.3 (OUT), TLS handshake, Client hello (1):
TLSv1.3 (IN), TLS handshake, Server hello (2):
TLSv1.3 (IN), TLS handshake, Encrypted Extensions (8):
TLSv1.3 (IN), TLS handshake, Certificate (11):
TLSv1.3 (OUT), TLS alert, unknown CA (560):
SSL certificate problem: unable to get local issuer certificate
Closing connection 0

另外，运行sudo pro status命令时也返回了证书相关的错误：

Failed to access URL: Canonical合约服务的资源查询接口
Cannot verify certificate of server
Please check your openssl configuration.

实在不知道哪里出问题了，有没有大佬能给点思路？

谢谢大家！
Jimmy

备注：内容来源于stack exchange，提问作者Jimmy