Mac: 'The operation could not be completed' when trying to update the signature

You get this error when trying to update the signature for Mac Mail in Mac OS:

Please try creating a signature in Apple Mail manually in the following way:

1. Start Mac Mail.
2. Press Cmd + ',' to open the settings.
3. Click "Signatures".
4. Create a signature by clicking the '+' button and enter some test.
5. Close the signatures dialog.
6. Quit Mac Mail by pressing Cmd + 'Q'.

Run the "Update all signatures" from the Xink menu.  

If you are still getting the error please check your iCloud settings as described here:

http://support.xink.io/support/solutions/articles/1000227905-setting-up-your-icloud-drive-for-the-mac-os-xink-app