How would I force the certificate renewal via the command line?
Per Linode:
1.) Your Linode does have a private IP. I’m not exactly sure what the issue might be or what they mean by “export”
2.) Hey there, Yes that looks correct! The extra zeros aren’t an issue, with IPv6, you can keep or remove the extra zero’s. Here is a link that gives you some more insight on that: https://networklessons.com/ipv6/shortening-ipv6-addresses/ Just to clarify: [IPV6 address with :0000:0000:] & [IPv6 address] Are the same IPv6 address 
I’m not sure why Mail in a Box adds them with the zeros, but there is no need to be alarmed there. Please keep in mind that since we are an unmanaged hosting provider, troubleshooting this issue is a task for your systems administrator or developer. If you have any other questions, please feel free to reach out to us at any time. Kind Regards, HM Linode Support
Per Google Domains:
Dennis So, in your web host’s end, there’s a setup that’s somehow expecting to resolve at [IPV6 address]. You see, as your registrar, we only point your domain name to the mapping information provided by your host.