hitch coupler lock for a jayco TT?

I use the Diversi-Tech (DT) shown above.

Thieves will just wrap chain around the stinger and tongue a few times and drag it down the road. They do not worry about lights or how it tows, they only need to go a short way and then they can take their time stripping all your belongings.

Better to make it much harder to drag away like a wheel boot or chains through the wheels. If it takes longer than 1 minute to grab they will move on to easier targets.

Another way to lock the hitch is to buy an extra ball, then cut off the shank, and lock in place with a padlock.

Not sure what you purchased, but here's what I've been using on 3 different TT's. I suppose it works, because I've never had a TT stolen. We purchased this one, years ago, through a small local company that built utility trailers.

Internet images.

I haven't found one that fits either. I've got one that doesn't fit good but I rig it on there with a cable tie. It doesn't lock it at all but maybe they'll see it from the road on move on. Better than nothing I guess.

I've been using a CURT Coupler Lock for years, don't bother with a lock through the coupler latch. That said, any lock will only keep honest people honest.