I finished a recent website project which took too much time for a low price. I delivered the project completed (without excluding potential minor bugs). After delivery, they informed me of something that I never knew before. It makes the main part of the project difficult to use and would need me to change it almost entirely.
As we talked about it months before, it would need someone else to continue the project if needed. They asked if the "additional" amount would be deducted from my initial price.
I refused as I delivered the project completed, the issue is coming from a missing important information; but is this something that a client can do ?
Edit: Sadly there is no contract or document describing the tasks. I worked at the client for a year when I was a student and we both thought I "knew the main issues" of the project. This is a huge mistake on my side, but I still got an information after the delivery.