My Apple Fitness app is not working on iPhone or Apple Watch, How can i fix this?

If you open the health App, tap on "Browse" in the right corner below, then tap on "Steps", scroll down to data sources, can you see your Apple Watch and your paired iPhone listed?

Did you make sure that on your iPhone in Settings/Privacy/Location Services is enabled for the Apple Watch, as well as Motion & Fitness for the Health App or any other app you are using to record your workouts?

Did you already try to unpair the watch, then pair it again to your iPhone, but this time setting it up as a new Apple Watch, without using the latest backup?

Unpair and erase your Apple Watch - Apple Support

Your iPhone is updated to the latest iOS 17.6.1 ?

Does the Apple Fitness App start and show no results, or do you get any error messages?

In case it does not start, did you try to delete the Fitness App and download it again?

Delete built-in Apple apps from your iPhone, iPad, or Apple Watch - Apple Support

Does your Apple Watch sync the Workout data to the Health App on your iPhone?

Use the Health app on your iPhone or iPad - Apple Support

If I open the Health App on my iPhone, tap on Browse/Steps/Show All Data, I can see the total amount of steps I took at this point. Taping on this number/date, I can see which steps the Apple Watch registered and which have been recorded by the iPhone.

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And my Apple Watch and iPhone are on the list of devices that can add data to the count of steps taken.