Symptoms
Even after you enable the Push Notification feature for the Skype for Business for iOS client in a Microsoft Skype for Business Server 2015 environment, the users of the Skype for Business for iOS still cannot receive notifications.
Cause
The IOS event channel doesn't respond to the request of Skype for Business for iOS when the event key in the request is case-sensitive.
Resolution
To fix this issue, install the March 2018 cumulative update 6.0.9319.516 for Skype for Business Server 2015, Web Components Server.
