refactor: add to index.d.ts & change MFACode type

src/errors/Messages.js

@@ -11,6 +11,8 @@ const Messages = {
   TOKEN_INVALID: 'An invalid token was provided.',
   TOKEN_MISSING: 'Request to use token, but token was unavailable to the client.',
 
+  MFA_INVALID: 'An invalid mfa code was provided',
+
   WS_CLOSE_REQUESTED: 'WebSocket closed due to user request.',
   WS_CONNECTION_EXISTS: 'There is already an existing WebSocket connection.',
   WS_NOT_OPEN: (data = 'data') => `WebSocket not open to send ${data}`,