Unfoturnately, Amazon does not sync highlights on books that have not been purchased on Amazon. This is also why Readwise cannot automatically sync those highlights.
Hi, thanks I did not know Readwise. I signed up for an account to check how it works. It uses a browser extension to sync the highlights instead of using the API. It can sync automatically but your browser must stay open (which is OK IMHO). Readwise can sync much more sources also.
Thanks for introducing me to Readwise, I might use it :)