Kindly refer from the heading above I failed to send email 
I FAILED TO SEND EMAIL IN OSTICKET PLEASE HELP ME
Also Here Is myError message
The error is pretty clear, you are using invalid (incorrect) credentials.
You are also using an unsupported version of osTicket. To receive any further assistance please upgrade to one of the latest supported releases (v1.18.1 or v1.17.5).
Cheers.
Also I would recommend consulting the documentation for setting up gmail.
https://docs.osticket.com/en/latest/Getting%20Started/Email%20Settings.html