Make sure access to API is enabled in the Google Admin Portal.
To enable API access, log in to your admin account, and select Security.
Under Access and Data control > API Controls
Click in Manage Google Services
Make sure the google services are unrestricted, specially Google Workspace Admin and Google Sign In.
Retry the Connection with ODME
Once the connect is made, test the connection with a valid email address in the Google Environment, if the connection fails do the following:
Log in to your admin account, and select Security.
Under Access and Data control > API Controls
Scroll down to Domain Wide Delegation
Click in Manage Domain Wide Delegation
Click Add new in API Clients
The Client ID and OUTH scopes can be found in ODME > Connections
Click Authorize and test the connection again in ODME