Warning: call_user_func() expects parameter 1 to be a valid callback, function

Question

I keep getting this error when. I am trying to insert a dashboard widget and I don't know what's causing the error.

Warning: call_user_func() expects parameter 1 to be a valid callback, function 'voguepay_woocommerce_payouts_dashboard_widget_display' not found or invalid function name in C:\xampp\htdocs\9ja\wp-admin\includes\template.php on line 1037

here is the code to add the widget

     public function register_voguepay_woocommerce_payouts_dashboard_widget(){
    add_meta_box(
    'withdraw_to_bank',
    'Withdraw to Bank',
    'voguepay_woocommerce_payouts_dashboard_widget_display',
    'dashboard',
    'side',
    'high'
);



}

public function voguepay_woocommerce_payouts_dashboard_widget_display(){

echo "Hello World, I'm a great Dashboard Widget"; 
     }

Answer 1

I just found the solution. use this code instead

        public function register_voguepay_woocommerce_payouts_dashboard_widget(){
    add_meta_box(
    'withdraw_to_bank',
    'Withdraw to Bank',
    array($this, 'voguepay_woocommerce_payouts_dashboard_widget_display'),
    'dashboard',
    'side',
    'high'
);



}

public function voguepay_woocommerce_payouts_dashboard_widget_display(){

echo "Hello World, I'm a great Dashboard Widget"; 
     }