The audio device ‘dictates’ the sample rate. Usually there is some control panel delivered with the device to set sample rate, buffer size etc.
Then there is setting the rate programatically. So in 95% of all cases, when Cubase tells the Performer to change its rate because it doesn’t match, it does that by asking the audio driver to do so. If that refuses the request, there is nothing we can do and it needs to be resolved manually. I don’t know how to do that on an iPad with Behringer hardware, sorry.