Installed Calsync but can't login

Installed Calsync but can't login

I have 2 factor authentication enabled. I generate a unique code to login to calsync. After many attempts, I still can not get in.  What I am doing wrong?

I have a samsung galaxy 7 and current have zoho mail working via a google  mail app. I now  want to have add access to my calendar.

Help!!!

Ruben