Not showing all added books

Hi

I have a kobo nia and i use calibre to add books to it.

i mark the books i want in calibre and select transfer/add to device. Then a green check appear in front of these books indicating that they are in the main of my kobo.

But.

Just a handful of the books show up to actually be able to read in Kobo. What am i doing wrong?
The books are all in epub format and they are ok to read through calibre

why isnt all the books showing in my kobo?

Im traveling in a few days and I would really like to bring a lot o f books with me on the trip.


TIA