Ah, fixed it by posting with python code in zapier. Probably a weird way to do it but it works...
import requests
api_url_follow = '{my_URL}/api/core/members/'+input_data['member_id']+'/follows/?key={the_API_key}'
todo_follow = {
"followApp":"core",
"followArea":"club",
"followId":int(input_data['club_id']),
"followNotify":1,
"followAnon":0,
"followType":"daily"
}
response = requests.post(api_url_follow, data = todo_follow)
700newtons's post in Using 'Post in Webhooks by Zapier' was marked as the answer