WooCommerce.
I have a customer who is planning on selling her newest book “Hverdagslykke” (Everyday Happiness). It is in Norwegian.
Shipping for 1 bok (1 book) = 85 Kr.
Shipping for 2 eller flere bøker (2 or more books) = 120 Kr.

Result quantity of 1:

Result quantity of 2 or more:

I am using the code on this site: sjelefode.no (sjelefode = food for the soul.)

I have been searching for a way to adjust shipping charges that change when quantity changes.

I have been following this tutorial:
https://businessbloomer.com/woocommerce-setup-tiered-shipping-rates-order-amount

In the bacckend.
WooCommerce -> Settings -> Shipping ->  the customers shipping zone is Norway. I hovered over the Zone name Norway and using the quick edit bar selected Edit. Here I adjusted 1 shipping method and added a new title and Cost of 85. Then Made another shipping method where I also adjusted the title and added the Cost of 120.

I then went to functions.php and pasted the following code:

add_filter( 'woocommerce_package_rates', 'bbloomer_woocommerce_tiered_shipping', 10, 2 );
function bbloomer_woocommerce_tiered_shipping( $rates, $package ) {
$threshold = 2;
if ( WC()->cart->get_cart_contents_count() < $threshold ) {
unset( $rates['flat_rate:6'] );
} else {
unset( $rates['flat_rate:1'] );
}
return $rates;
}

NB! To find the correct flate rate ids. In the frontend in the cart. Right click the shipping and select Inspect (Element) to see the HTML and CSS used on the page. From inspecting I could see that the flat rate id is 6 for more then 1 book. To find the flat rate for 1 book I would then adjust the quantity in the cart and then right click shipping to find the correct flate rate id here as well.

A tip.

Sometimes the cache can be really slow to refresh.
1. To refresh WooCommerce go to in the backend: WooCommerce -> Status -> Tools. Then just click to clear transients. (I just clicked the various buttons to be sure that the cache was cleared.)
2. If needed open Inspect. Right click the browser and open Inspect. Move the cursor on top of the refresh half circle icon (top left beside the URL line) and hold down the mouse button and select “Empty Cache and Hard Reload.”

The above techniques should clear the cache so you can see the newest adjustment.