I finally figured it out and wanted to pass along just in case others had the same issue.
As I mentioned before, although Windows showed that there was a listener going on port 80, I couldn’t get a cert. (Let’s Encrypt it needs to validate the domain.) What I learned was that Axigen was not the listener and could not be enabled: Since Axigen was not the listener on port 80, it could not obtain the certificate from Let’s Encrypt via Axigen.
So what I decided to do was bind the non-SSL Listener to port 8080 and it enabled without a problem. I then forwarded port 80 to 8080 on my router.
Once I did that, I was able to have Axigen generate a new SSL certificate, which I then bound to the different listeners.