Changing WooCommerce cart item names

The goal is to change the name of the item as it gets passed to our payment gateway, but leave it as-is for display on our product pages.

I've tried this in my functions.php:

function change_item_name( $item_name, $item ) {
    $item_name = 'mydesiredproductname';
    return $item_name;
}
add_filter( 'woocommerce_order_item_name', 'change_item_name', 10, 1 );

But it doesn't seem to be working for me. I feel like I should be passing in an actual item ID or something… I'm a little lost.

Any information on what I'm doing wrong here would be greatly appreciated.