Please fill out the fields below so we can help you better. Note: you must provide your domain name to get help. Domain names for issued certificates are all made public in Certificate Transparency logs (e.g. crt.sh | example.com), so withholding your domain name here does not increase secrecy, but only makes it harder for us to provide help.
My domain is: bstpoc.serviceconnect.defence.gov.au
I ran this command: using Certify the Web. Screenshot attached.
Upon initial inspection, my inkling is that your webserver configuration was recently changed in such a way that Certify can't properly present the HTTP-01 challenge file for Let's Encrypt's validation servers to find.
When using IIS Certify will automatically configure everything, when using Apache you have to configure the Site Root Directory under Authothorization > http-01 to point to your Apache htdocs path so that the app can populate the /.well-known/acme-challenge path of your site, you also need Apache to serve any of the files that are presented there and not redirect to an application or content management system.
I also note that your domain is behind Azure Application Gateway so you may need to check you are forwarding http requests directly to your server.
A basic test for http domain validation is to create an extensionless text file under the /.well-known/acme-challenge path of your site, then try to access it via http from a remote network. You need to have that working before you can complete an http challenge.
