After installing the Gmail App:
- Access the Google Admin App console to check whether the CAS App has been enabled for all users:
- Check whether the provisioned user has CAS App installed by clicking on the Google Apps button. Trend Micro Cloud App Security should exist there.
- Check the Google Admin page about the advanced G Suite API setting:
- On the Google Admin console, go to Security > Settings.
- Refer to this G Suite Admin help article to enable API access, then check the apps for Gmail.
- Ensure Trend Micro Cloud App Security has permission for Gmail.
For reference, check Provisioning a Service Account for Gmail.