Problem connecting a speed/cadence sensor to my vivoactiv 4S

I will not get into a debate over the speed & cadence "worthless" point of view. I do think that you will find many people, pros even, that will disagree with you.

I agree with 4411990, the speed and cadence on spin bike is as important as on an outdoor bike.

If you have a spin bike in mind, I suggest you ask Garmin before buying it.

On my side, I have to use Wahoo app to get the data of cadence and speed, send the data to dropbox and then import the data into Garmin connect. A big workaround to have my data into Garmin .  Plus, I don't have the exact dimension/circumference of the flywheel of my Matrix ICR50. So, the numbers look a little bit weird. I asked Matrix to give me the dimension of the flywheel: no answer yet. So, I'm thinking to may be buy wahoo sensors. But, again, I don't know I could install the speed sensor on that spin bike because the flywheel is at rear... All that because my Garmin vivoactive 4S can not connect to bike sensors.  Unbelievable.

Yeah, I have an old spin bike with a flywheel that I mounted the speed sensor on, can even measure the circumference and input the numbers, and a cadence sensor. This setup works great for me, but she wants something modern.

I also have an old trainer with another set of Garmin sensors, but that setup is getting old. But she doesn't like that either. I need to keep the peace so buying it is.

We are going to look at a few this weekend and see in person if they connect to her watch. Support centers now-a-days is worthless, maybe better luck with sales people, although I'm not counting on it. So a real test will tell the story.

I'm thinking the Garmin apps need ANT+ coming in. That's just not right for today's spin bikes. But I doubt they will change, at least not on the Vivoactive 4/4S line....

I didn't say that cadence was useless, and I guess the pros are using power sensors. My point is that speed and distance are rather useless on a stationary bike without it, since you can't control resistance. Without reference, you could just as well use bananas as a unit for the speed and distance. 
Other than that clarification, I will not derail the discussion further.

Confirmed, it is ANT+, and the HR broadcast is also ANT+.

This is probably the reason:
ANT+ is designed and maintained by the ANT+ Alliance which is managed by ANT Wireless, a division of Dynastream Innovations owned by Garmin.