Hi Richard, thanks so much for using Codebook and sorry for the trouble.
while scanning the QR code I get on the Windows version (via Add A New Device) using the iPhone’s camera returns “no usable data found”
Sorry that this isn’t clearer: it’s not the Camera app on your iPhone that you need to launch to scan the QR code being displayed by Codebook for Windows, instead the Codebook app on your iPhone needs to do the scanning (not the Camera app).
In your case, since it sounds like it would be easiest to stick with the Sync Key you created on Windows,
launch Codebook on your iPhone and sign in. Then go to the Sync tab (under the More tab). There, use the Delete Sync Key option to whack the local Sync Key on your iPhone, and confirm the ominous-sounding prompt. At that point, the Sync view should now be displaying the option “Setup Sync Key”. Tap that, and you should see the “Setup Sync Key” view, with the prompt to create or scan a Sync Key–select “Yes” (you have already created your Sync Key, on Windows) and Codebook for iPhone will access the camera so you can scan the Sync Key from Windows.
Please let us know if that helps!