Please make sure to reduce your code to a minimum working example (MWE) that reproduces the error that you’re seeing and that others can run, have a look at: Please read: make it easier to help you
If I copy the code in your post above, I get the error newPoints not defined, which occurs on the very first line of your deCasteljauPoints function (where you do append!(points, newPoints), without defining newPoints first)