As stated in the question, we have a sub who was paid in full and he submitted his signed unconditional with a zero balance and then 3 days after that, he sent a bill for $30,000. There was no "contract", it was a time and material sub. We requested all subs and vendors to submit final bill and change orders. Then we paid all the submissions and requested signed, zero balance unconditional's after the checks cleared, in order for us to submit our package of unconditional's to the client landlord in order for us to get paid. We felt bad for him as he has been a long time sub and recently had a stroke so we paid half to him out of our own profit as the landlord was not going to give a dime towards this bill and stated he had a signed unconditional zero balance from this sub. Now this sub wants to sue us for the remaining $15,000. The last 4 projects he has worked on all had major issues that has cost us thousands to fix and feel if anyone should be sued it should be this sub. What does the law state?