You cannot add "Cisco Business 350 Series 350-8FP-2G - Switch - L3 - Managed - 8 x 10/100/1000 (PoE+) + 2 x combo Gigabit Ethernet/Gigabit SFP - rack-mountable - PoE+ (120 W)" to the basket because the product is out of stock.
Cisco C9300L-STACK-KIT= StackWise Switch Stacking Kit for Catalyst 9300L Series