Although it is a paid version of shift work calendar which is currently discontinued, it will be unusable in the next iOS 11 scheduled to be upgraded this autumn.
We recommend you to move to the free version.
Please refer to the following article on taking over of data and add-ons.
If you update the OS to 11, the application (paid version) will not start, so please do so before updating the OS.
Please note that if you update the OS before migration, you will not be able to take over the add-on purchase situation with the paid version.