Postmates is responsible for every order you put through their website because they are the intermediary and most of the time their couriers (the ones we talked about above) deliver the orders, not the restaurant and with anything, any kind of problem arising, you have to contact Postmates.
If there is a refund or something else, Postmates will give you the best deal you can get, and they will solve the problem in the background between them and the restaurant.
This is the good part of ordering from a platform like Postmates because they handle everything for you in case of a mishap.