curl --request POST \
  --url https://api.example.com/api/v1/contacts/groups/{group_id}/members \
  --header 'Content-Type: application/json' \
  --data '
{
  "contact_ids": [
    "3c90c3cc-0d44-4b50-8888-8dd25736052a"
  ]
}
'

import requests

url = "https://api.example.com/api/v1/contacts/groups/{group_id}/members"

payload = { "contact_ids": ["3c90c3cc-0d44-4b50-8888-8dd25736052a"] }
headers = {"Content-Type": "application/json"}

response = requests.post(url, json=payload, headers=headers)

print(response.text)

const options = {
  method: 'POST',
  headers: {'Content-Type': 'application/json'},
  body: JSON.stringify({contact_ids: ['3c90c3cc-0d44-4b50-8888-8dd25736052a']})
};

fetch('https://api.example.com/api/v1/contacts/groups/{group_id}/members', options)
  .then(res => res.json())
  .then(res => console.log(res))
  .catch(err => console.error(err));

{
  "success": true,
  "added": 123,
  "member_count": 123
}

{
  "detail": [
    {
      "loc": [
        "<string>"
      ],
      "msg": "<string>",
      "type": "<string>",
      "input": "<unknown>",
      "ctx": {}
    }
  ]
}