fab agreement (4a)

It is not on Fab Distribution Agreement but in Marketplace Distribution Agreement, I wonder why they are using it instead of Fab Distribution Agreement.

Note- I am not Lawyer

Here is simpler Explanation, You as Seller is selling Digital Right (Product) to Epic Games, and Epic Games is Reselling that Digital Right to Customer. So as Reseller Epic can charge Customer any Price (Higher or Lower then Base Price that you had Set for Selling) It is kind of their flexible right as a Reseller.