Monzo is experiencing technical issues affecting certain functionalities of its app, leading to the implementation of a temporary backup service called Monzo Stand-in. Users reported difficulties with the app, with over 3,000 outages noted on DownDetector. Despite the issues, customers can still check balances, make card payments, withdraw cash, freeze cards, and send or receive bank transfers. Monzo is actively investigating the problem and working on a fix to restore full service.