This repo demonstrates how to use the servant-quickcheck and servant-checked-exceptions libraries together. In order to use both libraries, an instance of HasGenRequest (Throws err :> rest) needs to be defined. Here is simple way to define that instance:

instance (HasGenRequest rest) => HasGenRequest (Throws err :> rest) where
  genRequest _ = genRequest (Proxy :: Proxy rest)

Check out test/Spec.hs for more detail, or clone this repo and run stack test to verify that this works.