I've been having an issue getting books onto my Kobo since around the time of the 8.0.1 Caliber release. I would send books to the Kobo, the sync job would run, I'd get a green check that it was transferred, but when disconnecting none of the synced books showed up!
Been searching the internet for solutions to the problem, never found anything accept some suggestions to wipe and start over. It's been a frustrating couple of months, but since I have a few hundred books already on the device, it was fine, but I really wanted to read this new purchase.
So I fixed the issue, and it's working again. What happened is I enabled parental controls back when I got the Kobo, so I could put a PIN on the device to unlock it. I then disabled the PIN needed when opening the device, but parental controls were still enabled.
A feature of parental controls in the Winter 2024 update is it blocks side loading!!! See here:
https://www.kobo.com/blog/kobos-wint...ures-and-fixes
This feature change happened to be around the time I updated Calibre to v8.
Wanted to share this in case someone else runs into the issue. I search the forum and couldn't find a mention of this.