Sideloading kepub from Android is not picked by Kobo

I have Calibre installed in Termux on android, I use it on the command line. I installed the kepub output plugin. I download the economist with a recipr when on the road.

Downloading epub and mobi works. When I connect the phone and kobo with USB-C cable and put them into the root directory I see there, they get picked up by Kobo. But with Kepub, Kobo does not see the file. Any idea why? I am genuinely puzzled.