- Is this your corporate iPhone? Then please contact the system administrator of your corporate
- If it is your personal device, in that case, do you have any profile installed by your corporate/organisation/enterprise/School Management?
- Erase the profile added by you If you have installed a profile on your own --> Install or remove configuration profiles on iPhone - Apple ...
- Or please contact the system administrator of the organisation who provided the profile to you

When you have activated 2-step verification/Authenticator for your Microsoft Exchange/Outlook, Yahoo, Google Mail, AOL account, it introduces an additional layer of security, preventing the use of your regular login password when accessing your account through a web browser. In such cases, you are required to generate a unique and device-specific application password for use on iOS devices.
To accomplish this, navigate to the provided link, which facilitates the creation of an iOS app-specific password. This distinct password ensures a secure and seamless connection between your iOS device and your Microsoft Exchange/Outlook account, Yahoo, Google Mail, and AOL allowing you to navigate the heightened security measures while maintaining the convenience of accessing your email and other services on your iOS device.
You may have enabled two-step verification on Google --> Sign in with App Passwords - Google Account Help
You may have enabled Authenticator for Yahoo --> Generate and manage third-party app passwords | Yahoo Help
You may have enabled 2-step verification for Outlook/Hotmail --> Manage app passwords for two-step verification
You may have activated 2-step verification for AOL --> Create and manage third-party app passwords - AOL Help