I only have a basic understanding of DNS and I am trying to redirect HTTP requests to this website to HTTPS requests.
letsencrypt advises that my "www" has an A record with IP address but my "non-www" does not and advises to add an A record for the "non-www" to solve the problem as it is unable to create certificates.
This site is hosted by linode.com which has instructions on how to set DNS records but these instructions do not match the options offered by linode to set DNS records.
These options are only to leave the field blank or enter the domain name only (endoldpoliticsnow) and are not valid entries for letsencrypt.
If there is a third option, of which I am not aware and cannot find any hint in linode docs (or anywhere else for that matter), it is likely to be a cryptic one I cannot guess.
Linode.com used to have a true ticket system but appears now to post any ticket/question on the Internet and hope someone will volunteer an answer.

Can someone make a suggestion on how to solve this problem?

Attachement is a screenshot of the A/AAAA records as shown by linode.com.

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A quick look at your DNS from one of my servers shows that www and non-www are both pointed to 139.162.23.155 so please post the full output from letsencrypt, along with what commands (etc.) you are using to try to obtain the cert.

After a night's sleep, it works now, it looks like it was a matter of slow propagation.
My apologies for the distraction.

I have also received a similar response from linode.com so my perception of their disappearing ticket system was incorrect.