Long, around 6-7 inch seed pods should form after flowers go over. They are ripe when they turn brown in late summer or early fall.

Not every flower will produce a pod.

Ah, looking very carefully, I see that the remaining tiny receptacle that the flower left behind is expanding at places where flowers have fallen off. i guess that's going to grow into a seed pod later on.

Well, I was told that seed pods should form. It's fall now, and NO seed pods have formed. Not a single one. These plants were absolutely bursting with flowers, and we have loads of pollinators around. What happened? Someone told these flowers not to form seed pods. Would eventually like to get a couple of seeds from these plants. Ideas?

OK, mystery resolved. THIS YEAR I'm getting a lot of seed pods. It would seem that crossvine needs some maturation before it decides to produce seed pods. In fact, I'm guessing there were a couple last year, because I have a new crossvine plant coming up a few yards away.