Unable to install a Let's Encrypt certificate for a domain in Plesk: Invalid response. "unauthorized" and not able to open document root via File Manager

Symptoms

• Unable to install Let's Encrypt certificate for a domain in Plesk:

  PLESK_ERROR: Error: Could not issue a Let's Encrypt SSL/TLS certificate for example.com.
  The authorization token is not available at http://example.com/.well-known/acme-challenge/TEVVIggXJr2wIfgXHswrVzKhY_Vl4FRDlg8gxE9jeFg. 
  To resolve the issue, make it possible to download the token file from the URL above. 
  See the related Knowledge Base article for details. 
  Details 
  Invalid response from https://acme-v01.api.letsencrypt.org/acme/authz/0X3TgeS_0p0S_-gUjxcFpIX7KUgr0RBgSQ3J4HNmadY. 
  Details: 
  Type: urn:acme:error:unauthorized 
  Status: 403 
  Detail: The key authorization file from the server did not match this challenge [TEVVIggXJr2wIfgXHswrVzKhY_Vl4FRDlg8gxE9jeFg.uprcbKEM_iGGF4EfQso0mx1-pelsk forkYBMfN6vybiR7TJS114] != []

• Unable to access the domain's document root at Plesk > Domains > example.com > File Manager:

  PLESK_ERROR: Unable to open the directory: Unable to find the directory C:\Inetpub\vhosts\example.com\httpdocs\: Access denied

Cause

Incorrect permissions for domain's document root.

Resolution

1. Connect to the server via RDP.

2. Open File Explorer and navigate to the domain document root.

3. Right-click on the directory and choose Properties

4. Select the Security tab and click Advanced

5. Verify that the permissions of users are as follows:

   

   And the Special permissions of IWPG_exampleuser:
   

Additional information

It is possible to set permissions via the command line, however, command requires caution and experience. For example, in order to set user jdoe full control to httpdocs, all subfolders, and files, the following command can be used:

C:\> icacls "C:\inetpub\vhosts\example.com\httpdocs" /grant "jdoe:(OI)(CI)(F)" /t