Du kan få en hel liste.
978-87-415-6418-9
978-87-17-04200-1
978-87-412-5198-1

978-87-412-6264-2
978-87-929-1400-2
978-87-7702-568-6 Denne findes allerede i mit bibilotek på Zotero, men kan stadig ikke fremsøges via ISBN

Det lader til, at programmet bare skulle trues lidt. Efter genstart (hvilket jeg ellers har prøvet i går) så fungerer det igen. Mærkeligt...

(3)(+0000000): HTTP GET https://www.worldcat.org/api/search?q=bn:[…] failed with status code 403

You're being blocked by WorldCat, where the data for that ISBN comes from (and it works for me). That could happen if you've been adding lots of items via ISBN. It might also just be intermittent — WorldCat changed their site in a way that makes it much harder for Zotero to retrieve metadata. Try again later and see if it works.

The main way of saving to Zotero — via the web browser:

https://www.zotero.org/support/adding_items_to_zotero#via_your_web_browser

You can likely even save from the WorldCat site.