What type of ids do i need to use when adding custom entity types to an answers experience?

What type of ids do i need to use when adding custom entity types to an answers experience?
I have created entity types named “attendee” and “session” but i’m still getting an error when trying to add them to the entity types list in an answers config.

  • Entity type id is invalid: attendee
  • Entity type id is invalid: session

I figured out that custom entity type ids are always prefixed with ce_