Here are a few of the most common fixes to issues people have when syncing with no specific error message.
1) Make sure you have your Apple Watch selected as your source for steps in the Fields tab. Do not select Apple Health or iPhone unless you use your phone as your main source of steps and don't use an Apple Watch.
2) Syncing will only work if you have your active Apple Watch selected. If you have multiple Apple Watches in the Fields tab and you're not sure which one to pick, you can try a sync with each one, or you can change the name of your watch with our guide.
3) If you don't see any steps at all in Fitbit, only calories, you may need to connect a Fitbit to your account. This is an easy fix even if you don't have the Fitbit - please see our guide here.
4) Make sure you have the right app. Each myFitnessSync app only syncs in one direction. The red app, "Sync for Apple Health > Fitbit" syncs from Apple Health/Watch to Fitbit. The blue app "Fitbit to Apple Health Sync" goes from Fitbit to Apple. If you purchased the wrong app, reach out to support at the top right of this page with "submit a request".