WooCommerce redirect after add to cart

wc-redirect-after-add-to-cart.php

/**
 * Redirect to checkout at add-to-cart action.
 */
function redirect_to_checkout() {
	return WC()->cart->get_checkout_url();
}
add_filter( 'woocommerce_add_to_cart_redirect', 'redirect_to_checkout' );


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/**
 * Redirect to checkout at add-to-cart action on specific product IDs.
 * When not in the list of IDs it will go to the cart (default behaviour).
 */
function redirect_to_checkout_product_ids( $url ) {
	if ( in_array( $_REQUEST['add-to-cart'], array( 1, 2, 3 ) ) ) :
		$url = WC()->cart->get_checkout_url();
	endif;
	return $url;
}
add_filter( 'woocommerce_add_to_cart_redirect', 'redirect_to_checkout_product_ids' );