- Plesk for Linux
- Unable to install Let's Encrypt SSL with "404 not found", "Timeout", "Could not connect" or "400" errors:
<title>404 Not Found</title>
PLESK_ERROR: Error: Let's Encrypt SSL certificate installation failed: Challenge marked as invalid.
Could not connect to example.com
PLESK_ERROR: Error: Could not issue a Let's Encrypt SSL/TLS certificate for example.com. Authorization for the domain failed.
- Domain has A record for www.example.com, but not for example.com
Incorrect DNS configuration for a domain.
- Verify that domain name, e.g.
wwwprefix resolves globally. Use MXToolBox online checker:
If not, modify domain's DNS on a registrar side so that domain resolves to Plesk IP globally
- If domain resolves to both IPv6 and IPv4, make sure that the both IP addresses are configured in Plesk Domains > example.com > Web Hosting Access
If it is not possible to add IPv6 address in Plesk, than remove AAAA record from a global DNS for a domain;
Try to install Let's Encrypt certificate again.