Fixed Amount and Set Selling Price are two different options of Discount settings in the app. Check the below examples to see the difference between the two.
Fixed Amount: With the Fixed amount discount settings you can give amount off on the bundle you have formed with the product/s.
For Example: There is a bundle of two products A and B, and you want to sell the bundle of two products at $10 OFF discount then Fixed Amount option from Discount Settings is used.
Set Selling Price: Set Selling Price option in discount settings is used to sell a bundle at one price.
For Example: There are two products A and B, and you want to sell the bundle of two products at selling price $30. Then you have to Set Selling Price as $30.