There’s very little info to work with so it’s unlikely you’ll receive any specific advice.
But mainly you do want to be fully connectable (port forwarded) so check that. Go to any port test website (www.canyouseeme.org, www.yougetsignal.com/tools/open-ports/, etc.) and enter your torrent client’s incoming connection port there. (for qBittorrent that is in Tools / Options / Connection / Listening Port)
If that test fails then you need to figure out what is blocking your torrent client’s incoming connection port.
If you’re using a proxy that’s the issue, won’t get an incoming connection port via proxy
If you’re using a VPN service that does not support port forwarding then that’s the issue, it is impossible to port forward on a VPN without port forwarding support
If you’re using a VPN service with port forwarding support then go to their website & figure out how to configure it, each VPN service is slightly different
If you’re not using a VPN/Proxy then most likely you’ll need to log into your network router/firewall & configure a port forward there. Basically create a port forward for your torrent client’s incoming connection port & point it to your local system on the network (your NAS)
Also make sure to whitelist your torrent client in any anti-virus/malware software you are using, those will definitely slow you down and/or block connections to your torrent client.
There’s potentially other issues but everyone starts with being connectable first.