curl --request POST \
  --url https://www.postable.com/api/v1/projects/add-recipients/{projectUuid} \
  --header 'Authorization: Bearer <token>' \
  --header 'Content-Type: application/json' \
  --data '
{
  "recipients": [
    {
      "first_name": "John",
      "last_name": "Doe",
      "address": "123 Main St",
      "city": "Anytown",
      "state": "CA",
      "zip": "12345",
      "country": "United States",
      "email": "john@example.com",
      "internal_id": "CUST-001"
    },
    {
      "first_name": "Jane",
      "last_name": "Smith",
      "address": "456 Oak Ave",
      "apt": "Suite 100",
      "city": "Othertown",
      "state": "NY",
      "zip": "67890",
      "country": "United States",
      "override_message": "Custom message for Jane"
    }
  ]
}
'

{
  "data": {
    "message": "<string>",
    "contacts_updated": 123,
    "contacts_created": 123
  }
}