[self.client loginCustomerWithCredentials:credentials callback:^(BUYCustomer * customer, BUYCustomerToken * token, NSError * _Nullable error) {
            if (customer && !error) {
                self.appDelegate.cart = [self.client.modelManager insertCartWithJSONDictionary:nil];
                NSLog(@"Success fully loged in token %@ %@",token.accessToken,token.customerID);
                UINavigationController *navigationController = self.navigationController;
                [navigationController popViewControllerAnimated:YES];

            }else{
                [self showEror:@"LogIn Failed" message:@"Please provide valid Details"];
            }
        }];

In the above code after a successful login I try to create a cart for the user. I then add items to cart, but when I close and reopen the app the cart is empty.

How do I create a cart for the user so then they are able to access it on any device?