FLStudioMobile requires iOS 8.0 or later, the highest supported iOS on iPad (1st generation) is 5.1.1
You will need an iPad 2 or higher to use FLStudioMobile 3. However we would recommend a 3rd generation ...
FLStudio for desktop. This allows you to transfer your MiniSynth presets to FLStudio and get the same sounds. Alternatively you can just use MiniSynth inside the FLStudioMobile Plugin that also runs inside FLStudio ...