This is the best approach but we can understand the frustration if it's taking longer to accept. But you can't do anything if you will stay on that project and wait for them until they pay. If having an idea that they won't be paying or the pay you get is a bit lower than what you have expected, there is nothing you can do with that. There are more good projects that will come out or if there is no more projects that are good like the older days, keep moving on and it will help you improve picking the correct one.