BlackMartin

yes, Air staff is correct regarding port forwarding - my mistake
 
to others who find this topic...
 
AirVPN - go to your control panel and forward a port for both UDP and TCP - leave the fields blank and it will auto-pick a port
 
make sure the port you use is NOT forwarded in your router
 
there is no need to forward this port anywhere else (firewall, router, etc.) other than in the AirVPN control panel
 
qBittorrent > tools > options > connections
listening port - plug in the same port you forwarded on Air
uncheck UPnP
uncheck use different port on each start
 
qBittorrent > tools > options > connections > connection limits
global max = 100
connections per torrent = 50
(settings above suggested by Air staff)
 
qBittorrent > tools > options > bittorrent > privacy
enable DHT
enable PeX
 
qBittorrent > tools > options > advanced
network interface = tun0 (on Linux anyway) - you may have to be connected to the VPN before the tun0 option is available
 
if you change VPN servers, you may have to repeat the above step if you are unable to download
 
also see: Do you allow p2p? How can I optimize performance of eMule and BitTorrent with AirVPN? - Sales - AirVPN (https://airvpn.org/faq/p2p/)