Why isn't the Mobile App not letting me sign in to my account?

What devices are you all using?  Is the app up to date?  Have you tried uninstalling the app after deleting the app cache and app data?  If your OS version is beyond the support window of the device.  That might be why the app is not working.  Much older versions of iOS and Android have many security holes that can easily compromise the data and security of the app.