Hi, first of all great piece of software, i have tried various rival softwares and this is by far the best IMHO, well worth the pro licence.

However, I have been scratching my head for days but I am finding it impossible to connect to nzbdrone/couchpotato when my server is connected through a VPN. I have setup a ddns address, which is working when the server is not connected to VPN.

Anyway I'm quite new to this (servers/networking etc.) so any help would be great. Also let me know if I can provide any extra details.
You sure you don't mean when your CLIENT is connected ? I assume you have a vpn server running on the same machine as the services (couchpotato, nzbdrone, etc), and you want to connect your phone/tablet to that server to access these services.
eh is the vpn server yours ? or is it a 3rd party subscription ? If it's yours, you might need to enable client-to-client communication. I don't know if that is possible using a subscription though because of security reasons.
yeah it's a subscription and I had kind of been thinking that but that's quite annoying if that is the case. Would there be no way round that? As I would want my download traffic to go through the VPN even if nzb360 could connect outside of the VPN...
well I believe the services should still be available on the 'home' IP address regardless whether it's connected to a VPN server. So if you have forwarded the ports and connect to IP:PORT (where IP is the actual server's IP address, not the VPN assigned IP), it should still work.