Plesk Let's Encrypt Plugin - Issues with Obtaining Certificate

Can anyone throw any light on this error message…?

Server is a Linux dedicated server.

Error: Let’s Encrypt SSL certificate installation failed: Challenge marked as invalid. Details: Invalid response from “<!DOCTYPE html>
<!–[if IE 6]>
<html id=“ie6” lang=“en-US” prefix=“og:”>
<!–[if IE 7]>
<html id=”


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My domain is:

I ran this command:

It produced this output:

My web server is (include version):

The operating system my web server runs on is (include version):

My hosting provider, if applicable, is:

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

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

The Domain is:
Ran Command: approx 17:00hrs BST (that is UK time)
Output: the Error Message
Web Server: Linux running Plesk
OS: CentOS 6.9
Hosting; Fasthosts
Root Shell: Yes
Control Panel: Plesk Onyx v17.5.3

We need to know which command you ran. How did you envoke the client to try to get a certificate?

Logged into server (

Navigated to Let’s Encrypt Extension

Added the Domain (

Ticked the two boxes and clicked the button…

Then the Error came up…

Hi @Nemysys, this sounds like a bug in Plesk or in your configuration of it. I think you'll need to ask Plesk support because so far no Plesk developers are participating in this forum, and they are probably the only ones who can fix this.

If you're comfortable with command-line system administration, you could also try one of the other clients, since you have a dedicated server.

However, they would probably not integrate very cleanly with Plesk.

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