I have tried many times to rectify the problem of adding my Zoho email to my iPhone Mail app. I have followed the exact steps in this configuration ( https://www.zoho.com/mail/help/idevice-access.html) but it still doesn't work.

I keep getting the message 'username/password is incorrect'. 

I have checked my username and password and it is all correct. I have gone through all the necessary checks and it is exactly as what you guys said. 

I don't know what to do next and I'm getting tired of trying anymore.