fix function call

booking.stripe.inc

@@ -143,7 +143,7 @@ function booking_stripeform_form($form, &$form_state) {
  * Tries to add final validation after all else has been added through alters.
  */
 function booking_stripeform_add_final_validation($form) {
-  $form['#validate'][] = 'stripeform_validate_form_payment';
+  $form['#validate'][] = 'booking_stripeform_validate_form_payment';
   return $form;
 }