Hrm dual doesn't connect to ant+ fitness trainer

I've bought a hrm dual hartrate band cause of compatibility with the vivioactive4s. A side for using it with the watch I also want to link it to my  virtufit row trainer. Where my old polar band directly gives an hartrate the garmin hrm dual doesn't show any data.

I haven't connect it via ant with the watch at the same time. 

Anyone an idea what might be the case