No transmitted audio - IPad mic option disappears

I have SmartSDR for iOS connected to my Flex 8400 using a 6th generation iPad Pro.
When i start the app, the iPad mic option appears, but when i click PTT no audio goes to the radio. The level meter shows activity as normal, the radio goes into transmit, but the RF meter does not move and no RF comes out of the radio.
The DAX is off, but if i switch it on and then off, the mic window goes MIC. If i PTT, i get a message telling me I’m not using the iPad mic, but then the iPad mic option disappears. The only way to get it back seems to be to restart the app, but then the same thing happens again.
Also, when I first start the app, if i click on iPad MIC, it then just shows two options, mic and acc, with no iPad option or possibility of getting back to iPad without disconnecting and restarting the app.
TUNE works to initiate tuning on my tuner. The only missing seems to be getting the audio into the radio.
Any ideas?