Here's what I'm trying but it doesn't compile:

```
{-# LANGUAGE TypeFamilies #-}
{-# LANGUAGE StandaloneDeriving #-}
{-# LANGUAGE FlexibleInstances #-}

import Data.Text as T
import Data.Int (Int64)

type family Incoming validationResult baseType
type instance Incoming Validated baseType = baseType
type instance Incoming ValidationErrors baseType = Either [T.Text] baseType

data Validated
data ValidationErrors

data Tag = Tag {unTag :: T.Text} deriving (Eq, Show)

data NewTag f = NewTag
  {
    ntClientId :: Incoming f Int64
  , ntTag :: Incoming f Tag
  }

deriving instance (Show baseType) => Show (Incoming Validated baseType)
deriving instance (Show baseType) => Show (Incoming ValidationErrors baseType)

```

Compilation errors:

```
23  38 error           error:
 • Illegal type synonym family application in instance:
     Incoming Validated baseType
 • In the stand-alone deriving instance for
     ‘(Show baseType) => Show (Incoming Validated baseType)’ (intero)
24  38 error           error:
 • Illegal type synonym family application in instance:
     Incoming ValidationErrors baseType
 • In the stand-alone deriving instance for
     ‘(Show baseType) => Show (Incoming ValidationErrors baseType)’ (intero)

```