https://support.grokker.com/hc/en-us/articles/360000423472-How-do-I-connect-my-Fitbit-Garmin-or-Google-Fit-account-with-Grokker

How Fitbit works with Grokker:
When you connect your Fitbit account with Grokker, Fitbit activities from up to 48 hours ago will be sync'd. Going forward your workouts will be automatically sync'd with Grokker.
We specifically record activities tracked by devices. To ensure accurate tracking, please start your device, choose the workout, end the workout when done and press save. Manually entered activities are not included on Grokker.
Our focus is on the following Fitbit Activities: walk, run, bike, swim, sport, hike, elliptical, aerobic, training, exercise, and fitness.
It is worth noting that we do not sync steps from Fitbit.