Note that, in some circumstances,
ASIdentifierManager returns an invalid
advertisingIdentifier of all zeros . You (this is the case as of iOS 10 if limit ad tracking is enabled). You should use an alternate identifier instead of this invalid IDFA. Additionally, we recognize that the availability of UDID is somewhat tenuous. When our preferred identifiers are unavailable, a valid (non-zero)
UIDevice on iOS 6.0+) or a random identifier that's persistent with the app installation are acceptable.