I have added Privacy - Photo Library Additions Usage Description & Privacy - Photo Library Usage Description.
But none of the keys is asking for user permission to access the photo library.
I have tested in Simulator as well as in real device.
I even tried by adding a single key at a time. Like only Privacy - Photo Library Additions Usage Description or Privacy - Photo Library Usage Description. And also tried by adding both the keys together.
But none of the above scenarios is working for me.
I also added Privacy - Camera Usage Description and that's working perfectly fine. But photo library usage is not asking for user's permission
Any help is appreciated!

After iOS 10, if your app is using
PHAsset, PHPhotoLibrary, and PHImageManager, then you need to includeNSPhotoLibraryUsageDescriptionin app's Info.plist file.Detail info is available here: apple-ref-documentation