Probably, and most likely. If you have a really good reason, and just being broke isn't always good enough, you need to petition the court to change the payments to reduce them or do something, anything, to show good faith. The problem is you need to hire a lawyer when your money should go to paying restitution.
It depends on how restitution was ordered and if it was part of a sentence following a guilty finding or part of plea agreement. I you have the funds and are failing to pay you are more likely to be sentenced to jail or prison as part of the original sentence than if you cannot afford to pay anything.