There was an article about this subject but I not too clear about it.

In the Proxy part of the setup, I entered my NordVPN's torrent proxy credentials under TCP. Despite the same fields available for UDP, Tixati wouldn't work at all unless NO PROXY is selected. Where it says Incoming and Outgoing Peer Connection Protocol, I tried all options and keep getting the same results.

Ipeak.net and similar sites all report a fake IP address. However, both the fake and the REAL IP are visible in the swarm. Is there any way to fix this other than having to go back to µTorrent? I absolutely love Tixati and its colorful interface, but if my real IP is visible I can't use it. Some time ago before I had a VPN/proxy, someone apparently saw it and reported me, so my ISP sent me a warning email.

Bittorrent has:
TCP for transfers and (HTTP/S) trackers
UDP for transfers and UDP trackers and DHT peer discovery.

If you don't have UDP working, you will absolutely require HTTP-based trackers and PEX to discover peers. You can disable UDP in connection settings and separately DHT. This will castrate your client but should remove communication that bypasses the TCP proxy.

Tixati is one of the few if not the only client with advanced support for UDP proxies. The ball is on your side because few offer UDP proxies.

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You already have a VPN why do you want to use a proxy. Enable the VPN on the same machine as Tixati and go to Tix settings to force lock Tixati to the VPN network interface for Ipv4 and Ipv6