I’m creating my second app in React and I’ve stumbled upon a problem I can’t really solve. Here are my codes (front-end, back-end and one of my tables): https://jpst.it/3MnNs. The problem is my *deleteBook* function is not working. Before, after clicking on the deleteBook button, my server kept crushing with the error message saying: *invalid input syntax for integer: “undefined”* and now, for some reason, the button doesn’t work, like at all. Everything looks right to me and to be totally honest, after and hour of thinking about a solution, I’ve ran out of any ideas I had.

I really need help with this project and I know it’s a lot of code to go through so I’ll be thankfull for any feedback!