Can't reserve seats for Christmas

Hello,

I am trying to reserve seats for my Christmas holiday with my 4-day pass, but I am getting an error message when I go to pay for the seat reservations.

My trips are from Copenhagen to Munich on 27 Dec and Munich to Zurich on 30 Dec.

I found the trains I would like to take, and I go through the steps to reserve, but at the end, it says I cannot book certain parts of the trip.

I don’t understand what I am doing wrong. I don’t think that the trains are full, because I went to the DB website, and it shows that there are seats available.

Any help would be greatly appreciated!