Unable to set up Exchange email on my iPad

Presumably you are trying to add a Microsoft email account to the native Mail App.

Some email providers now require the use of App Specific Passwords when accessing mail over IMAP or POP3. If this applies to your email account, you will need to generate a unique password for your iPad email account - that will differ from your normal Account Password. As examples - AOL, Yahoo, Google, Microsoft all use App Specific Passwords when using anything other than their own email client Apps. 

Microsoft accounts include - amongst others - live.com, outlook.com and hotmail.com domains.

If you need to generate an App Specific Password, you’ll need to log-in to your Mail Providers account management webpage - using a web browser - and generate the Password from the appropriate account security page.

More details about Microsoft App Passwords can be found here:

https://support.microsoft.com/en-us/account-billing/using-app-passwords-with-apps-that-don-t-support-two-step-verification-5896ed9b-4263-e681-128a-a6f2979a7944

nealfrompiedmont wrote:

Apple Mail will not accept my credentials when setting up Exchange email. It had been working.

It's not Apple mail, it is Microsoft that isn't excepting it. You probably need to use an app specific password or 2 factor authentication when using a 3rd party app to access your exchange account.

Contact microsoft support or look at their help forum for more help.