Google has phased out the "allow less secure apps" setting, that allowed connecting to your mailbox via IMAP/POP using your Google account password.
..and then use this app password for the IMAP/POP connection inside the helpdesk system.
To generate an app password go to your google account settings - security - scroll to the bottom and select "search google account" - type "app password" into the search box - create app password.
IMPORTANT: the app password Google creates for you is a 16-letter code. You have to remove spaces before entering it into Jitbit (or any other app), just copying-pasting won't work!
If your app password has stopped working all of a sudden - generating a new one should help.