PolRail is just a private travel agency that may in some cases also organise some train tickets-hardly ever those with only RES as they earn on ticket sales, not on the xtraś.

At ARRival there go to the busy with people in he same situation as you counter in Keleti station (under renovation-buildings works all over), show pass, tell waht you want (you also did not here-like seat/sleep or what day, so make up mind before)-do not worry-they have seen/heard it thousands of times before.

Yes, alas in the very distant past even most of those burocratic state-rail-´companies´ were working more closely together and were often able to organise this for you in remote areas-but thats now mostly a thing of the past. has to do with whom organises the IT-systems and what is linked to it. PLUS that most are only aimed at selling normal all-in tickets and to prevent fraud by people only paying for the RES some working person has to actively override that system to get it done