error case: creating user with duplicate email, return json with msg for toast

lib/routes/api/users.js

@@ -370,7 +370,7 @@ router.post('/', async(req, res) => {
     const email = allUsers.find((e) => e.email === payload.email);
     if (email) {
       logger.debug({payload}, 'user with this email already exists');
-      return res.sendStatus(403);
+      res.status(422).json({msg: 'user with this email already exists'});
     }
 
     if (decodedJwt.scope === 'admin') {