Hey @siriusly
Thanks for using Codebook and reaching out. The sync protocol changed in Codebook for macOS 4.1.0 and we discontinued support for version of macOS older than 10.12 in Codebook for macOS 4.3.0
I’ve just messaged you directly with instructions for downloading an old version of Codebook for macOS (4.2) that supports both your version of macOS and the new sync protocol.
If anyone else is running into a similar issue, please reach out to our support at support@zetetic.net