Add these to your list of trackers. The order and spaces are important. UDP is preferred since it uses less resources so should be added first. The IPv4 and IPv6 trackers are different servers so need to be seperated by two line breaks to use both.
udp://ipv6.pow7.com:80 https://ipv6.pow7.com/announce http://ipv6.pow7.com/announce udp://ipv4.pow7.com:80 https://ipv4.pow7.com/announce http://ipv4.pow7.com/announce
The previous tracker URLs are still functional, but only provide either IPv6 or IPv4 peers, depending which is used to connect.
udp://pow7.com:80 https://pow7.com/announce http://pow7.com/announce