A favor.

Kindred society never managed to come up with an internal form of currency. Some interesting Vitae based experiments were held, but most were eventually exposed as evil schemes to bring forth Gehenna, which sort of discredited them. So the closest thing to money the Kine have, is favors.

This means that the returning of favors is regarded as a very important thing. Ignoring a boon that was given is perceived as a threat to “our way of life”. Some places actually have Harpies to uphold this issue, but the natural intolerance of vampiric society is usually enough.