I have tried to pair several different HR monitors to Zwif iOS version. Including Vivosmart HR+, Mio Alpha, Mio Slice and Garmin Fenix 3 HR. All set in broadcast mode. I have tried via both Bluetooth and ANT+. But the app does not want to recognize the heart rate monitor. The Tacx Neo sensor is recognized correctly It even wants to connect to my speed, cadence and Stages sensors (though I do not want those on Zwift). So the app is not very good at finding HR monitors.
Right now I am using a Garmin Edge 520 to collect the training data for TrainingPeaks. But it would be nice if this could be done using the iOS app.