nginx container seems unable to reach OSC responder *LetsEncrypt): how to debug

Very new to docker, I’m trying to setup an nginx docker that uses https with a LetsEncrypt certificate that is already existing and working correctly outside docker. Within the container it raises an error that seems to be related to reachability of external host from within the container:

nginx_1    | 2019/11/29 00:10:03 [warn] 1#1: "ssl_stapling" ignored, host not found in OCSP responder "ocsp.int-x3.letsencrypt.org" in the certificate "/etc/letsencrypt/live/customersite.it/fullchain.pem"                                                      

nginx_1    | nginx: [warn] "ssl_stapling" ignored, host not found in OCSP responder "ocsp.int-x3.letsencrypt.org" in the certificate "/etc/letsencrypt/live/customersite.it/fullchain.pem" 

I’m using nginx:latest . How can I debug if the container can in fact reach ocsp.int-x3.letsencrypt.org? ping is not available nor ‘host’, but a request from outside reaches correctly port 80, that makes me think the networking is correctly setup (default bridge).