How to fix bus error at pop function in C?

Question

I'm trying to reverse a word in C with the implementation of stack. For example, If ı call the reverseArrayfunction with the parameter string "Ali", then function should reverse the word and make it "ilA". The problem is when I try to Pop the value from stack, a bus error occurs.

Here is the stackstruct.

struct stack
{
    int top;
    unsigned capacity;
    char *ar;
};

Here is my reverseArray function:

void reverseArray(char word[])
{   // Length of the given word.
    int loe = strlen(word);
    printf("%d",loe);
    struct stack* stck = createStack(loe);
    
    int i;
    for (i = 0; i < loe; i++) 
    Push(stck, word[i]); 
    
    // This is the line bus error occurs.
    for (i = 0; i < loe; i++)
    word[i] = Pop(stock);
    
}  

Here is my Pop function:

char Pop(struct stack* my_stack)
{
    if (isEmpty(my_stack))
    {
        
        return 0;
    }

    return my_stack->ar[my_stack -> top--];
}

Here is my Push function.

void Push(struct stack* my_stack, char val)
{
    if (isFull(my_stack))
    {
        printf("Overflow!!!!!!");
        return;
    }
    my_stack -> top += 1;
    my_stack->ar[my_stack -> top] = val;
}

Here is my isEmpty function

int isEmpty(struct stack* my_stack)
{
    return my_stack -> top == -1;
}

and here is my createStackfunction

struct stack* createStack(unsigned capacity)
{
    struct stack* newStack = (struct stack*)malloc(sizeof(struct stack));
    newStack -> top = -1;
    newStack -> capacity = capacity;
    newStack -> ar = malloc(newStack -> capacity * sizeof(char*));

    return newStack;
}

I believe the problem is in the Pop function. If I delete the Pop part of the code in reverseArray function, function works fine. Feel free to ask more information.