Hi @yibo,
Thank you for your responses.
I suspect that the Auth0 Action does not allow any way to call the event.user.groups property since it is not a part of the callable properties.
Because you can get the user’s "groups" using the Management API, I suggest calling the Management API within your Action script to be used for your logic (e.x appending to custom claims).
Please see our How can I use the Management API in Actions? FAQ to learn more.
In this case, you will need to call the ManagementClient getUser() method to retrieve the user’s profile.
Please let me know if there’s anything else I can do to help.
Thank you.