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Birthdayz 2
Birthday
What date is the next birthday on a common year for a date of birth on a leap day?
February 28 is the next birthday on Birthdayz.
What date is the next birthday on a leap year for a date of birth on a March 1?
March 1 is the next birthday on Birthdayz.
Badge and Alert
There is a case that the number of birthdays is displayed on the app icon even though there is no birthday.
There is a case that the number of birthdays is displayed even though there is no birthday within the target period set in the Badge setting in this app. This is a designed behaviour of iOS 11 and later. As a result, the number displayed when there are birthdays continues to be displayed when there is no birthday.

The number of birthdays on the app icon will be displayed correctly by launching the app. Sorry to trouble you, but please launch the app once when the problem occurs.
The number of birthdays is not displayed on the app icon.
When there are no birthdays within the period you set, the number of birthdays is not displayed on the app icon.

If the Badges setting (Badge App Icon setting on iOS10 and iOS11) in the Settings app > Birthdayz > Notifications is disabled, the number of birthdays is not displayed on the app icon.
No alert is displayed even when the time to show an alert has come.
If the time you set has come immediately after you quit Birthdayz, no alert may be displayed. It is impossible to deal with this issue due to technical restriction.

On iOS10, if you set the ALERT STYLE WHEN UNLOCKED setting to “None” in the Settings app > Birthdayz > Notifications, no alert is displayed. Similarly, if you disable the Show on Lock Screen setting, no alert is displayed if the time has come during a lock.

On iOS11, if you disable the Show as Banner setting in the Settings app > Birthdayz > Notifications, no alert is displayed. Moreover, if you disable the Show on Lock Screen setting, no alert is displayed if the time has come during a lock.

On iOS12, if you disable the Lock Screen, Notification Center, and Banners settings in the Settings app > Birthdayz > Notifications, the corresponding alerts are not displayed respectively.
Though the Badge and Alert settings are set properly, the icon badge and/or alerts are not displayed.
You need to set notification settings of Birthdayz also in the Settings app > Birthdayz > Notifications. Be sure to check and change the settings.
Notification is not done correctly after updating iOS.
Please launch Birthdayz once after updating iOS.
View
Some information related to birthdays such as ages and days from birth are not displayed.
If a date of birth is yearless, information which need year information to know them are not displayed on the Birthdays screen and the Info screen.

On the other hand, Chinese Zodiac is not displayed if the year of a birthday is not between 1870 and 2030 in the gregorian calendar and if you select the “Japanese (Lunar)” calendar used to determine Chinese Zodiac. This restriction is a designed behaviour of this app.
Can I set the region format and calendar of dates displayed on Birthdayz?
Yes, you can. The region format and calendar used by Birthdayz are dependent on the Region and Calendar setting of the Settings app > General > Language & Region. So, by setting these settings, you can set the region format and calendar used by Birthdayz. Please note that these settings are also used by other apps.
Import from Contacts
Some contacts with birthdays are not listed on the Import screen.
From iOS8, you can add Chinese, Hebrew, and Islamic birthdays to your contacts, but Birthdayz does not support them. Therefore, contacts with birthdays in these calendars are not listed on the Import screen.
Others
Can I use some URL scheme for this app?
You can use an URL scheme to launch this app. The scheme is “birthdayz”.
Can I use this app on a jailbroken iOS?
As you know, jailbreaking is a violation of the Apple's end-user license agreement (EULA), so this app is not guaranteed to work on such environment.

Please see the following page about jailbreaking.
http://support.apple.com/kb/HT3743