square.onBookingCustomAttributeDefinitionOwnedDeleted subscribes to booking.custom_attribute_definition.owned.deleted for the selected seller. It does not require an additional Square OAuth permission.
Example
automations/square-on-booking-custom-attribute-definition-owned-deleted.automation.ts
Event
A custom attribute definition owned by your application was deleted. Note that only the definition owner can delete a custom attribute definition. The signal resolves to the officialSquare.BookingCustomAttributeDefinitionOwnedDeletedEvent payload with type narrowed to booking.custom_attribute_definition.owned.deleted.