Don’t spend your own money on a friend or family member’s pet project unless you’re willing to consider that money a gift if you need to.

The ‘cousin’ part is the part that’s tripping him up here. Any other business venture telling you “I can only afford to pay you if you redo it” could be met with a retort of, “That isn’t the terms of our contract. If payment is not rendered according to our contract, I’ll be seeing you in court.”