Cannot issue Let's Encrypt certificate on a Plesk server: The service is down for maintenance or had an internal error

Symptoms

• Cannot issue Let's Encrypt certificate:

  Error: Let's Encrypt SSL certificate installation failed:Could not obtain directory: Invalid response.
  Details:
  Type: about:blank
  Status: 503
  Detail: {
  "type": "urn:acme:error:serverInternal",
  "detail": "The service is down for maintenance or had an internal error. Check https://letsencrypt.status.io/ for more details."
  }

• The token file mentioned in the error message can be successfully downloaded:

  # wget http://example.com/.well-known/acme-challenge/lTfAocUiE6LIgowBVQHScbfifG6xLocn3pOhLrMGdK4
  HTTP request sent, awaiting response... 200 OK

• Let's Encrypt service status at https://letsencrypt.status.io/ is Active Incident.

Cause

Let's Encrypt service is temporarily unavailable.

Resolution

Monitor the Let's Encrypt service status at https://letsencrypt.status.io/ and try to issue the certificate again when it becomes available.