Update error message for CPEx auth error (#3837)

* Update error message for CPEx auth error

* undo the hasMessage change

Author: ravern

website/api/nus/auth/login.ts

@@ -36,7 +36,7 @@ const handlePost: Handler = async (req, res) => {
 const handleError: (error: Error) => Handler = (error) => async (_req, res) => {
   res.status(500).json({
     message:
-      'An unexpected error occurred. Please try clearing your browser cache and logging in again. Follow the NUS login page instructions carefully.',
+      'An unexpected error occurred. Please try logging in with your NUSID, in the format nusstu\\e0123456, instead of your email. You can use Incognito mode or clear your cookies to try again.',
     error,
   });
 };