Create an authorization in Email Security - Cloud.
Select Configuration > Authorizations.
Click Add Authorization.
From the platform drop-down, select Google Workspace.
Enter an authorization name and description(optional).
Click Create.
The authorization configuration page opens.
Next to Status, select Manage.
Under Admin email, enter the email address of the owner of the pub/sub topic you created earlier. This user will be granted owner status of the auto-generated subscription object.
Under Topic, enter the Topic Name of the topic you created in the Google Cloud pub/sub configuration.
Under Credentials File, upload the JSON file saved by your browser when you configured the key associated with the service account you created in Google Cloud.
Click Save. The authorization status is now "Authorized."