Sharing the advance payment when one wants to cancel

Shalom.

A group of young men rented a place for Shabbat and paid an advance. One of them wants to cancel—does he have to pay his share?

Shalom and blessings.

He must pay.

Regarding the obligation of one for whom expenses were laid out on his word, see Shulchan Aruch, Choshen Mishpat, siman 14, Rema, se'if 5, Even HaEzer, siman 50, se'if 3. It is also possible that there is a kinyan kesef here; see siman 312, Sema, sk. 1. And it depends: if he has already given the money and from that the advance was paid, he has acquired through kinyan kesef. But if one person paid for everyone on the assumption that they would reimburse him afterward, it is likewise possible to say that they acquired via agency; see also siman 183.