You can set up two different types of discounts in your shopping cart configurations. The first is an item-level discount which is for a discount on a specific item. The second is a transaction-level (special reason) discount which is a discount on an entire transaction.
Both item and transaction-level discount configurations can be found by navigating to your gear icon > Configuration > Shopping Cart.
Item-level discount
Let's say you want to create a discount for your dog adoption fees for a special adoption event or create a discount for your collars for the holidays.
In the "Item-Level Discount Reasons" section, select the blue "Add Item Discount Reason" option. Then, add the discount's title and select the blue "Save" button.
Once you have the discount reason added, navigate to the appropriate adoption price group, select the blue "Edit" option on the right-hand side, and apply your new discount reason along with the dollar amount.
Going forward, every time that fee or item is added to a cart the discount will automatically be applied until you edit the fee or item again and remove that discount.
Transaction-level discount
Let's say you have a few consistent reasons you would discount someone's entire transaction like they had to wait a long time in line or maybe they're only able to pay part of the fee that you ask for with owner surrenders.
Regardless of the reason, the setup is very similar to the item-level discounts as outlined above. In the "Transaction-Level ("Special") Discount Reasons" section, select the blue "Add Transaction Discount Reason" option. Then, add the discount's title and select the blue "Save" button.
Once the discount reason is added, you can apply it to a transaction in your shopping cart, by entering the amount you would like to discount in the "Special Discount" box. Once you start the checkout process, you will see a pop-up that asks for the transaction-level discount reason.