Modify proceed to checkout button without shipping method in WooCommerce on your child site.
Snippet Type
Execute on Child Sites
Snippet
add_action( 'woocommerce_proceed_to_checkout', 'modify_checkout_button_no_shipping', 1 );
function modify_checkout_button_no_shipping() {
$chosen_shipping_methods = WC()->session->get( 'chosen_shipping_methods' );
// removes empty values from the array
$chosen_shipping_methods = array_filter( $chosen_shipping_methods );
if ( empty( $chosen_shipping_methods ) ) {
remove_action( 'woocommerce_proceed_to_checkout', 'woocommerce_button_proceed_to_checkout', 20 );
echo '<a href="'.esc_url(wc_get_checkout_url()).'" class="checkout-button button alt wc-forward">' . __("Alternate checkout text", "woocommerce") . '</a>';
}
}