square.onBookingCustomAttributeDefinitionOwnedCreated subscribes to booking.custom_attribute_definition.owned.created for the selected seller. It does not require an additional Square OAuth permission.
Example
automations/square-on-booking-custom-attribute-definition-owned-created.automation.ts
Event
A custom attribute definition was created by your application. The application that created the custom attribute definition is the owner of the definition and corresponding custom attributes. The signal resolves to the officialSquare.BookingCustomAttributeDefinitionOwnedCreatedEvent payload with type narrowed to booking.custom_attribute_definition.owned.created.