If your sync screen is completely blank instead of showing your cookbooks and other data files, that is often caused by a backslash character in a cookbook or recipe title.
Sign out of your online account in the sync manager program.
Check the cookbook names and make sure none of them have the backslash character \ in them.
Next, check the recipe titles. Go to the Search screen. Select the Expanded Search button near the upper right of the screen.
Type in the \ character.
Remove the checkmarks from Ingredients, Notes, and Serving Ideas.
Add a checkmark next to Titles.
Press the Add button in the lower center of the screen.
Then press the Search button.
Then it will show the recipes that have the backslash character that is causing problems. See the screenshots below.
You need to remove that backslash character.
Then go to the Cookbooks screen and select Refresh File List from the Tools menu to refresh the program and the sync manager. Now you can sign back into the sync manager and check if your cookbooks are now listed so you can sync them.