Snippet to redirect to checkout page after adding product to cart.

functions.php

/* Snippet to redirect to checkout page after adding product to cart.
Created at : 16 Jan 2019 PluginHive Plugins : https://www.pluginhive.com/plugins/
https://gist.github.com/renjith-ph/0defbaf8a48d49ec61fc50add6b1b051
*/
function ph_change_redirect_url_after_adding_product_to_cart( $url ) {
    $url = wc_get_checkout_url(); 
    return $url;
}
 
add_filter( 'woocommerce_add_to_cart_redirect', 'ph_change_redirect_url_after_adding_product_to_cart' );