IMAP - This feature is not available for your account

IMAP - This feature is not available for your account

I am unable to access my Zoho Mail account using IMAP.  The server returns the following error message -

You are yet to enable IMAP for your account

I checked mail settings in my account and under IMAP it says -

This feature is not available for your account

IMAP has been enabled and working for 10 years.  Why is it now not available?

Thanks for you help!