Pass correct context type with zValidator?

[hjaber]

How can I pass the specific context type from /register-user to my registerUser()? The default type c: Context results in a type error on valid("json")

app.post(
  "/register-user",
  zValidator("json", registerUserReqSchema),
  registerUser
);

async function registerUser(c: Context) {
  const validBody = c.req.valid("json");  // Argument of type 'string' is not assignable to parameter of type 'never'.ts(2345)
  const body = await c.req.json<NewUserReq>(); // works correctly
}

also tried to infer from c

auth.post(
  "/register-user",
  zValidator("json", registerUserReqSchema),
  async (c) => registerUser(c)
);

// c type for /register-user
//(parameter) c: Context<{}, "/register-user", {
//    in: {
//        json: {
//            email: string,
//            username: string;
//        };
//    };
//    out: {
//        ...;
//    };
// }>