PEM_read_bio_X509_AUX() failed (SSL: error:0909006C:PEM routines:get_name:no start line:Expecting: TRUSTED CERTIFICATE)

If you did a Discourse official Standard Installation and deleted everything and started over a bunch of times, you hit the let’s encrypt rate limit and can’t get a certificate for a week. You can bypass this if you follow Setting up Let’s Encrypt with Multiple Domains and add some other domain to the site. You could also just use a different name or wait a week.