Little more detail, the log reads;
[4/9/2020] [4:51:07 PM] [Express ] › 
warning Command failed: /usr/bin/certbot certonly --non-interactive --config “/etc/letsencrypt.ini” --cert-name “npm-14” --agree-tos --email “[email protected]” --preferred-challenges “dns,http” --webroot --domains “xxxxxx.duckdns.org”
Saving debug log to /data/logs/letsencrypt/letsencrypt.log
Plugins selected: Authenticator webroot, Installer None
Obtaining a new certificate
Performing the following challenges:
http-01 challenge for xxxxxx.duckdns.org
Using the webroot path /data/letsencrypt-acme-challenge for all unmatched domains.
Waiting for verification…
Challenge failed for domain xxxxxx.duckdns.org
http-01 challenge for xxxxxx.duckdns.org
Cleaning up challenges
Some challenges have failed.