A PNR with at least one itinerary segment must be in the Sabre work area

We are working with sabre APIs such as CreateSessionRQ, GetReservationRQ, AddRemarksRQ, EndTransactionRQ, CloseSessionRQ. we have gotton the reservation details using PNR locator through GetReservationRQ after creating the session with CreateSessionRQ. We have the following doubts:

1. While sending the request to AddRemarksRQ and EndTransactionRQ, there is no PNR is added to the request. We don't find the PNR locator in the sample request provided in the sabre developer website. How the PNR is associated with both the request ?
2. In the preconditions of EndTransactionRQ API, they are mentioned as 'a PNR with at least one itinerary segment must be in the Sabre work area'. Can anyone explain this?

When you call CreateSessionRQ you receive a BinarySecurityToken which identifies a sabre session. You then pass that BinarySecurityToken in the soap header of other saber web service requests.

When you call GetReservationRQ (in stateful mode), the PNR is loaded into the session identified by the BinarySecurityToken. Then when you call AddRemarksRQ, it will add the remark to the PNR that has was loaded in the session by the previous call to GetReservationRQ. The same applies to the EndTransactionRQ service call. It's the BinarySecurityToken that identifies the session that is acted upon by the stateful web service calls.