Error message (Failed authorization procedure) while trying to get certificate for subdomain

I have the domain with a let’s encrypt certificate up and running on my root server. However, following the same procedure in Plesk let’s encrypt extension for my subdomain, I get the error stated on the output section below.

The domain and subdomain are both targeted to the right IP address in the A records. The domain is also reachable, but I would like to get a certificate for this subdomain as well. I’m not sure how to read the error message though. I thought I have the DNS A Records set correctly.

Help is very appreciated! Thank you a lot!

My domain is:

I ran this command: plesk extension

It produced this output:

Error: Let’s Encrypt SSL certificate installation failed: Failed letsencrypt execution: Failed authorization procedure. (http-01): urn:acme:error:unauthorized :: The client lacks sufficient authorization :: Invalid response from "<!DOCTYPE HTML PUBLIC “-//IETF//DTD HTML 2.0//EN”>
<title>404 Not Found</title>
<h1>Not Found</h1>

  • The following errors were reported by the server:

Type: unauthorized
Detail: Invalid response from
<title>404 Not Found</title>
<h1>Not Found</h1>

To fix these errors, please make sure that your domain name was
entered correctly and the DNS A record(s) for that domain
contain(s) the right IP address.

My operating system is (include version): Debian 8.5

My web server is (include version): Apache 2.4.10

My hosting provider, if applicable, is: dedicated root-server location is hetzner

I can login to a root shell on my machine (yes or no, or I don’t know): Yes

I’m using a control panel to manage my site (no, or provide the name and version of the control panel): Plesk

for your domain ( ) if you place a file /.well-known/acme-challenge/test within the webroot - can you reach it in a browser ? (at )

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