Setup is Mac OS + Zwift App + ANT Dongle (incl. USB extension) + Garmin Speed + Cadence Sensor (the actual one). Garmin Connect App is installed but is not running (not even in the background).
Zwift recognizes the Cadense Sensor and shows the rpm correctly BUT it does identify the Speed Sensor but does not show any mph/kmh values at all ALTHOUGH my Garmin Edge + my Garmin Fenix are paired to the sensor and show any values correctly.
What goes wrong ?
For one ignore what the Edge and Fenix are displaying, that has nothing to do with Zwift.
Zwift will convert your rear wheel speed into watts, this will dictate your speed within Zwift along with your trainers power curve, elevation and your weight.
There is no powermeter at all (we are talking about a very, very simple rolltrainer with a dedicated Garmin Speed+Cadence Sensor) ?!
Again, Zwift will take the speed of your rear wheel and convert it to watts (virtual power/zpower) and that is how your speed is determined within Zwift. No power meter required.
You will NOT see the same speed within Zwift as your rear wheel speed.
You can vote my reply down if you wish, but I think you need a better understanding of the way Zwift works.
Please read: https://support.zwift.com/hc/en-us/articles/203968635–Setting-up-zPower-Classic-Trainer-Rollers?section=200993429
Ok, ok, I am sorry so if I understand it correctly: No powermeter or no classic trainer means no zwift ??!? (e.g. Spinning bike with Speed+Cadence Sensor) !?
You can use Zwift with a Speed and Cadence sensor, but your power will be estimated using the rear tire speed and the power curve of the trainer/rollers. With the power estimated Zwift will determine your in-game speed using the estimated watts, power curve of your trainer, in-game elevation, your weight, type of in-game bike and drafting within game.
Your in-game speed will usually not match that of your rear wheel speed that is why I said you should ignore what the Edge and Fenix are displaying.
There are a lot of people using just Speed and Cadence sensors within Zwift, hell that’s the way I started.