In iOS, a change was introduced from iOS 7.1, which requires that the OTA application be installed via HTTPS (not HTTP), and there are no provisions that allow the user to continue to accept the old behavior (i.e., allow the application to install via HTTP). I understand that this was done as a safety enhancement.
To install applications on iOS 7.1 from the Application Center, you need to configure your Application Center to use HTTPS, not HTTP, using a certificate that will be accepted as valid on your iOS device - that is, either issued by a recognized public CA or issued by a private The CA that you configured to use mobile devices. More information on how to complete this configuration can be found here:
http://pic.dhe.ibm.com/infocenter/wrklight/v6r1m0/topic/com.ibm.worklight.installconfig.doc/appcenter/c_ac_ssl_config.html
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