What do I do if the Mac tool isn't importing my Apple Book highlights?

Persistent spinning wheel or error:

Resolution:

1. Logout of the Mac tool
2. Select Resync to log back in and to run the sync again

Mac tool caveats:

1. The Mac tool only works for Big Sur and newer at this time. If you can't or don't want to upgrade the OS, then you can use the following instructions to get your highlights into Readwise --> How do I import Apple Books highlights from my iPhone/iPad?
2. The Mac tool cannot import highlights made on PDFs as Apple Books doesn't follow the PDF spec to create "real" highlights. You can use the following instructions to get PDF highlights into Readwise --> Can I import highlights from PDFs read in Apple Books?