I added this to my functions.php file :
add_filter (\'woocommerce_add_to_cart_redirect\', \'woo_redirect_to_checkout\');
function woo_redirect_to_checkout()
There are a few action hooks as well that you can use, for eg: woocommerce_add_to_cart which passes the product id to the callback function:
add_action( 'woocommerce_add_to_cart', 'custom_add_to_cart', 10, 2 );
function custom_add_to_cart( $cart_item_key, $product_id ) {
// replace 123 with a valid product id
if( 123 == $product_id ) {
wp_redirect( WC()->cart->get_checkout_url() );
exit;
}
}