Remove variable product from cart with ajax in woocommerce

Create the link on cart using the $cart_item_key instead of the $product_id.

Then, on server side, you don’t need to use the $cart->generate_cart_id($id); method, because you already have it.

See the example that works for me:

First, the creation of the cart:

// This is the logic that create the cart
foreach ( WC()->cart->get_cart() as $cart_item_key => $cart_item ) { ?>
    <li class="<?php echo esc_attr( apply_filters( 'woocommerce_mini_cart_item_class', 'mini_cart_item', $cart_item, $cart_item_key ) ); ?>">
        // Remove product link
        <a href="#" onclick="return js_that_call_your_ajax(this);" data-product_id="<?php echo esc_attr( $cart_item_key ); ?>">&times;</a>
        // Other product info goes here...
    </li>
<?php }

Now the modifications on server-side:

/**
 * Remove Cart via Ajax
 */
function product_remove() {
    global $wpdb, $woocommerce;
    session_start();
    $cart = WC()->instance()->cart;
    $cart_id = $_POST['product_id']; // This info is already the result of generate_cart_id method now
    /* $cart_id = $cart->generate_cart_id($id); // No need for this! :) */
    $cart_item_id = $cart->find_product_in_cart($cart_id);
    if($cart_item_id){
       $cart->set_quantity($cart_item_id,0);
    }
}
add_action( 'wp_ajax_product_remove', 'product_remove' );
add_action( 'wp_ajax_nopriv_product_remove', 'product_remove' );