Can't get email to work on my iphone, even after checking imap settings, etc. Sent emails for support.

Can't get email to work on my iphone, even after checking imap settings, etc. Sent emails for support.

I am new to zoho.  I started with the free account.  I took care of the domain verification and that was fine.  Then I created my email account.   I am able to send and receive emails on the web.  I can create additional accounts with my domain name, but I cannot get my iphone to work with mail or Thunderbird.  I have checked all of the imap settings, ports, etc.  

Still no luck.  The test accounts I created can do everything and work perfectly.  But my main account, the one that is admin cannot work at all for imap/pop3.   I've checked the password, etc.  

Am I missing something?  I would consider a paid plan but not if I can't get the free one to work.  I must be doing somethign wrong.

I forgot to add, the the zoho app works just fine on the Iphone but I would prefer to use the native email on the iphone.