It works for several scripts I have seen so I suspect that maybe you have the wrong announce url.
Please make sure that the syntax is correct.
Code:
http://mma-torrents.com/announce.php?passkey=
Code:
http://www.mma-torrents.com/announce.php?passkey=
or
Code:
https://mma-torrents.com/announce.php?passkey=
Code:
https://www.mma-torrents.com/announce.php?passkey=