Duckdns valide certificate but site not secured

Hi,
I followed the installation of Duckdns add-on. It was very simple.
Here is my configuration :

lets_encrypt:
  accept_terms: true
  certfile: fullchain.pem
  keyfile: privkey.pem
token: ***
domains:
  - ***.duckdns.org
aliases: []
seconds: 300

However, chrome tells me my site is not secured but also that my certificate is valid. I checked and it is indeed using Let’s Encrypt certificate.
image

Does anyone know how to fix this ?
Thanks :slight_smile: