group_id
user_id

curl -X POST \
-H "Authorization: Token d37fa8c4e008fec158070b1b4aea5f0db3d6a06e" \
-H "Content-Type: application/json" \
-d '{"group_id":"5", "user_id":"22"}' \
-k https://your.domain.com/api/users/add_user_to_group

{"status": "success"}