Access Next Cloud from outside of the network

I have installed Nextcloud 16.07 as a snap of Ubuntu.
I manage to access the IP of the NextCloud from the internal network, but I can not access it from outside the network.

  1. I registered the IP address of the host with a hostname at the web site:
  2. I forwarded the port 80 and 443 at my Mikrotik Router.
  3. I created a Lookup Zone and a host with the IP address of the server at my internal DNS.
    But, until now no luck to access from outside.

What do you propose me to do?
Have you tried before the free to register the IP?