Reuvain & Dina get engaged and give the Shadchan, Shadchanus money. A few weeks later they break up. Does the Shadchan have to return this Shadchanus money? Suppose they never gave Shadchanus money, do they have to give Shadchanus money to the Shadchan?
Aruch Hashulchan Even Haezer 50:42 says that if a Shidduch is broken, the Shadchan does not have to return the Shadchanus.
Chut Shani Shabbos volume 3 - page 243 - #10 says if the Shadchan was not paid, and the wedding was called off there is a dispute between the Taz and Bais Shmuel Even Haezer 50:7:23 whether one gets paid in such a situation.
There have been communal norms about this sort of thing, I don't know all of them. But presumably the Star-K's program was designed to mirror a prevalent set of practices.
If the shidduch breaks up, chas v’shalom, before the wedding, Star-K is exempt from paying the gift.
Payment of the gift will be made by Star-K within 30 days after the chasana.
(The Star-K was essentially offering an additional shadchanus payment, modeled after whatever the families would normally pay.)