Ask for donation in checkout process

You might be offering free items for download on your site, but suggesting those who do so make a donation. This code adds buttons in the checkout process to allows users to optionally choose a range of donation amounts. In this example the amounts are $2, $5 and $10. You will need to set up these amounts as products and then add in the product IDs.

		/**
 * Ask for donation in checkout process
 */

add_action( 'woocommerce_review_order_before_submit', 'cc_checkout_donation', 9999 );

function cc_checkout_donation() {

  $product_ids = array(223, 224, 225); // IDs for products created for each of the donation amounts eg $2, $5 and $10
  $in_cart = false;
  foreach(WC()->cart->get_cart() as $cart_item) {
    $product_in_cart = $cart_item['product_id'];
    if (in_array( $product_in_cart, $product_ids)) {
      $in_cart = true;
      break;
    }
  }

  if (! $in_cart) {
    echo '<h4>Make a Donation?</h4>';
    echo '<p><a class="button" style="margin-right: 1em; width: auto" href="?add-to-cart=223"> $2 </a><a class="button" style="margin-right: 1em; width: auto" href="?add-to-cart=224"> $5 </a><a class="button" style="width: auto" href="?add-to-cart=225"> $10 </a></p>';
  }
}