It seems like UpWork failed to do due dilligence, and now wants to get somebody to pay for it. They frequently delay payments just because they await your valid

It seems like UpWork failed to do due dilligence, and now wants to get somebody to pay for it. They frequently delay payments just because they await your validation after all. So the fault is on their side, but they may try to twist your hand, since they are big company and you are dependent on them.