Possible reservation types for a line item or insertion order.

RESERVATION_TYPE_UNSPECIFIED Reservation type value is not specified or is unknown in this version.
RESERVATION_TYPE_NOT_GUARANTEED Not created through a guaranteed inventory source.
RESERVATION_TYPE_PROGRAMMATIC_GUARANTEED Created through a programmatic guaranteed inventory source.
RESERVATION_TYPE_TAG_GUARANTEED Created through a tag guaranteed inventory source.
RESERVATION_TYPE_PETRA_VIRAL Created through a Petra inventory source. Only applicable to YouTube and Partners line items.
RESERVATION_TYPE_INSTANT_RESERVE Created with an instant quote. Only applicable to YouTube and partners line items.