Another red flag is that the client is threatening to sue you for $100k but you only billed him $6k. Your maximum loss should be the $6k he paid you. But you

Another red flag is that the client is threatening to sue you for $100k but you only billed him $6k. Your maximum loss should be the $6k he paid you. But you do need to consult with a lawyer. You say you have another job? So you should be able to come up with the money to hire a lawyer. If he's sending you legal threat letters, you have to pay for a lawyer yourself. However, he could be bluffing. It seems weird that a guy would pay $6k on a software project and then $10k+ to sue those developers for not delivering. I agree with the other people that walking away is the right thing to do. The lesson is that fixed-bid projects are usually a bad idea for small freelancers.