Loosen the nut off & you should find a hole running vertically all the way through the bolt.
Strip the speaker wire a good inch or more & insert it into the top of the hole so its poking out of the bottom & tighten the nut all the way up.
If the entire terminal is rotating when you turn the nut that is supposed to tighten down on the cable then it wouldn't work. You may be able to out the unit and stop the entire terminal from rotating. Could be a nut or a solder connection needs work.
Could be a bad terminal too.