How can I adjust shipping costs per item in my print on demand business?

hey guys im using printful for a print on demand business but when i add 2 shirts to the cart the shipping doesnt increase just stays the same like its only for one item, how can i make it so it increase the price going off how many shirts are in the cart

how can i make it add an extra $4 to the shipping cost pre shirt added to the cart ?

Can be done easily using our app ShipMagic.

However, you do need CCS enabled on your store for our app to work.