Undo in C, copy struct

I'm new to C and I'm trying to simulate an Undo functionality for a problem. I'm using generic vectors defined like this:

 typedef void* Element;

    typedef struct {
        Element* elems;
        int size;
        int capacity;
    } Vector;

For this, I created a function called "Copy" that should return me a copy of the vector I'm passing:

Vector* copyVector(Vector *v) {
    Vector* rez;
    rez = createVector();
    int i;
    for (i = 0; i < getSize(v); i++) {
        Element el = getElem(v, i);
        add(rez, el);
    }
    return rez;
}

It works when I call it everytime to save the "before" vector... like when I try to apply an add or remove on my current vector, I call this copy function first on another vector called undoVec like this:

undoVec = copyVector(v);

I checked and it works but when I call my undo function... which should do the reverse of the code before:

v = copyVector(undoVec);

It's not working anymore. Doesn't do anything. It wont modify my vector v... which is really just a pointer I think

void undoVector(Vector *v, Vector *undoVec)

What am I doing wrong? why wont this functionality work? I can paste more code or give more info if required, thanks.

void add(Vector *v, Element elem) {
    if (v->size == v->capacity) {
        isFull(v);
    }
    v->elems[v->size] = elem;
    v->size++;
}

Element getElem(Vector *v, int pos) {
    return v->elems[pos];
}