Apple Health Kit not syncing with World Walking

Check that World Walking is enabled.  To do that, open the Settings app on your iPhone, then go to Privacy, then Motion & Fitness and check that the switch beside World Walking is enabled.

Once enabled, the World Walking app will automatically bank any steps recorded through Health Kit since you last used the app.

If it is enabled and you are still having problems, please try restarting your phone or re-installing the World Walking app.