If you have trouble installing iOS Ad Hoc version of your application on your test device, you should verify these three points:
1. 1/ Verification of the UDID
UDID means Unique Device IDentifer, it is like a serial number used to identify precisely your iPhone, iPod or iPad.
The Ad Hoc Version of your app can ONLY be installed on a phone having its UDID registered in the Apollo Apps back office.
There is an online help to show how to get the UDID of your device.
You need to check if the UDID of the device where you try to install the Ad Hoc, match with the UDID registered on the page Publish > Certificates > iOS .
If the device is not registered, make sure the back office is unlocked (if not, click Modify on the page Publish > Publication > iOS) and follow this online help.
2. 2/ Verification of the iOS version number
If the UDID of your phone is registered, but you still have trouble installing your test app, verify the iOS version number of the device.
The device version number had to be iOS 9 or above (versions inferior to 9 are no longer supported, so you won't be able to install the app on a device with iOS 8 for example).
3. 3/ Previously installed Ad Hoc version
If all the above is correct, and you still have trouble, make sure you don't have any previous version of your app is installed on your device.
If you have, uninstall it before trying to install the newest version again.
If after checking this three points you still have trouble testing your Ad Hoc version, please contact the support.