The Birthday list is a calendar list of all of your Facebook friends' upcoming birthdays. At this point there is not a way to manually add birthdays to the list as it is generated from Facebook.
There are a few reasons why some friends may not be on this list:
1. Only "Top Friends" are chosen to appear in the list.
- Top Friends are those whom you interact with the most on Facebook. You can change the setting to show all of your Facebook friends by going to: Settings>Friends' Birthdays>All Friends.
2. Friends have made their birthday private on Facebook.
- Only friends who made their birthday public to third party apps will appear in the birthday list. If your friends made their birthday private on Facebook, or if they have denied access to third party apps in their Facebook privacy settings, then their birthday will not appear in the birthdays list.
3. Changes to Facebook API
- Version 2.6+ in Sync.ME Android uses Facebook's new API, which restricts the amount of information we can receive from Facebook.