Access application from outside created on dokku

I’ve created a dokku droplet and deployed a node app: git@github.com:heroku/node-js-sample.git

After deploy I cannot access the app from the outside either by using the IP:PORT or the domain:PORT

Ping the IP I get a response:

64 bytes from IP: icmp_seq=0 ttl=55 time=37.963 ms
64 bytes from IP: icmp_seq=1 ttl=55 time=38.982 ms
64 bytes from IP: icmp_seq=2 ttl=55 time=44.458 ms

When ssh the server I can see that the app is up and running:

dokku apps:report
=====> node-js-sample app information
       App dir:             /home/dokku/node-js-sample
       Git sha:             4d7f659
       App cid:             d215f9544d7b
       Status:              running

Curl the application from the DO server I can see the response:

curl http://IP:3767
Hello World!

Curl the application from the outside and there is no response.

Checking opened ports by nginx:

netstat -tanpl|grep nginx
tcp        0      0 0.0.0.0:3767            0.0.0.0:*               LISTEN      7573/nginx -g daemo
tcp6       0      0 :::3767                 :::*                    LISTEN      7573/nginx -g daemo

No idea what I could do next. Any help is much appreciated.

Cheers