Ring app no longer accepts my login details on iPhone

Hi all, I recently installed a Ring video doorbell and allowed my iPhone (IOS 18) to supply a strong password. All was well until I changed to a more memorable password to avoid problems when accessing the doorbell on my PC, laptop and iPad 4. Now I can access the doorbell and settings via web browser on all devices and also by Ring app on my iPad 4, all using my one email address and the new password. Sadly, I can no longer login on my iPhone and just see the message "Sign in failed. Try allowing cookies in your browser settings and restart Ring app to continue". I've tried setting Firefox and then Safari as the default browser but it makes no difference. Alerts come through fine on my iPad 4 but I need them to do so on my phone as they did initially. I've deleted and re-installed the Ring app several times and rebooted the phone at every stage but some data remains as I see the "Sign in failed..." message before I've even entered anything on the login screen of the newly installed app. Can I clear all Ring and iPhone cached data?