Is Appen Pay Per Task

Hello, I have a friend working for appen, and they are having trouble understanding how the structure works, and their support will not email my friend back. So is it pay per task? It does not seem that way based on the invoice - it seems that they track the actual hour amount you spend on tasks. If this is true, once you get the number of tasks done they expect per hour, can you just chill until the new hour starts? Is there any incentive at all to work fast or efficiently? Thank you for your answers in advance.