iOS - is Motion Activity Enabled in Settings > Privacy > Motion Activity
Apple has a sample project that shows how to check and request access for all the various permissions (including Motion Activity) here. I suggest you take a quick look at that - it's pretty straightforward.
New in iOS 9, CMSensorRecorder(doc link) has a class method to check if your app is authorized for Motion & Fitness:
- Switft
class func isAuthorizedForRecording() -> Bool - Objective-c
+ (BOOL)isAuthorizedForRecording