If you have a license for BirdieSync 3.x, you may freely update your version of BirdieSync for one year after you initially registered. After this period you can still use these versions but may need to upgrade your license to be able to use newer versions, minor included, published after this period. BirdieSync needs to be constantly adapted to Thunderbird, iPhone or Android evolutions. Note that usually updating Thunderbird to a new major version requires a new version of BirdieSync which supports it.