Connection refused/reset when trying to reach NAS via FQDN

Installing and Using OpenWrt
17

OK guys, now my NAS is reachable from Internet.
Following steps were necessary:

  • Installation of VPN Policy Routing

  • FritzBox configured with non-standard HTTPS Port Forwarding to Router WAN Interface

  • VPR Policy configured.

  • NAS to WAN Firewall Rule, any protocol, any destination

  • Port Forwarding Rule from any source host, any port in WAN to NAS, non-standard HTTPS destination port

For now VPR Policy uses all ports (both source and destination) with destination to all networks. Does anybody know which port(s) is/are used for communication between NAS and DDNS?
I'd like to know it in case I would route BT traffic over VPN.