Bulk API 2.0 Returning 400 Error {"failures":[{"field":"fields","value":"ActivityID"}]}

I've read through the documentation and can't find out why I keep getting this error. My Python code is below, and the error I keep getting is: {"failures":[{"field":"fields","value":"ActivityID"}]}

If anyone has any suggestions, I would greatly appreciate it!

CODE:

import requests

auth_string = 'MyCompany\MyUserName:MyPassword'

auth = auth_string.encode('base64','strict')

url='https://secure.p03.eloqua.com/api/bulk/2.0/activities/exports'

data= {

"name":"Activity Export Test",

"fields":{

  "ActivityID":"{{Activity.Id}}"

  },

"filter":"'{{Activity.Type}}'='EmailOpen'"

}

headers = {'Authorization': "Basic %s" % auth}

r = requests.post(url, data=data, headers=headers)

print r.status_code

print r.text