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.
Old add-on takeover
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.
Shift Work Calendar (Paid Version) is not on sale now and not supported for iOS 9.
If you use it on iOS9, it might not work well.
Free version (now on sale) supports for iOS9.
You can restore data from paid version to free version.
How to restore , please see this page.
This up use Google Calendar API v2, but it is denied now.
So we are updating this application to use API v3.
Please wait until new version is released
When you can not authenticate your Google account, Please refer these pages.
If you use 2-Step Verification
Sign in using App Passwords
If you don’t use 2-Step Verification
Allowing less secure apps to access your account
Shift Work Calendar for Android was released!