Zoho won't connect with Gmail

I am getting an error message when trying to send email from ZohoCRM through my gmail account. It used to work sometimes but now won't work at all. I get the following error message in Zoho. How can I fix it? P.S. The error message says to log in to my web browser but I am logged in and I still get the error message.

Error while processing the request! Unable to connect SMTP server:smtp.gmail.com Reason:Authentication failed:534-5.7.14 Please log in via your web browser and then try again. 534-5.7.14 Learn more at 534 5.7.14 https://support.google.com/mail/bin/answer.py?answer=78754 fl15sm7474678pdb.92 - gsmtp