Logged Activities API not returning walking activities

[jamessnell]

I am calling
https://api.fitbit.com/1/user/-/activities/list.json?offset=0&limit=20&sort=asc&afterDate=2017-09-20

after syncing my fitbit steps and can see them in the fitbit web dashboard. Why would I get an empty list?

{
"activities": [],
"pagination": {
"afterDate": "2017-09-20",
"limit": 20,
"next": "",
"offset": 0,
"previous": "",
"sort": "asc"
}
}

Thanks in advance