Install TestFlight on old devices

Hi,
I would like to test my app on old devices to check compatibility, but if I try to install TestFlight on my iPad3 with iOS9.3.5 it say that is not compatible.
There is any procedure to install on old iOS versions?

Thanks
I have exactly the same issue. We have an app which is compatible still with iPad2 / iOS 9.3.5.
Trying to install TestFlight from the App Store on iOS 9.3.5 says it's not compatible.
Is an Ad Hoc build the way to do? How to get that build on to the iPad?
Having the same problem here. Would like to test compatibility on iPad mini Gen 1 / iOS 9.3.5 but cannot install TestFlight from the App Store. Any help would be greatly appreciated. Thanks.

The only way I found to install an old version of TestFlight onto my iPhone 4s (iOS 9.3.6) was to backup another iPhone 4s (iPhone #1) that already had TestFlight and then to restore the backup on the iPhone 4s (iPhone #2) that did not have TestFlight. After the restore was complete, the old version of TestFlight restored itself on iPhone #2. TestFlight still works perfectly on both iPhone 4s devices.

Install TestFlight on old devices
 
 
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