You have to tweak its settings to be able to record to WAV. You can do this through the cogwheel available on the main interface. If you can't find this option, then simply record to MP4 and tap on the file. A list with options will be available from where you can save the selected file to WAV or any other format since it already has a built-in converter.
Their support page don't offer anything about WAV troubleshooting or something related.